Top 10 Most Aggressive Dog Breeds (for Each Size)

Aggressive behavior in dogs can create problems for owners, especially people who have multiple breeds. This aggression has many causes, including genetics, territoriality, or training. Sometimes you can train a dangerous dog to be friendlier, but it’s not always the case.

If you’re looking for a guard dog, you might be looking for an aggressive dog breed specifically. Whether that’s your goal or something you’d prefer to avoid, understanding which dogs are most likely to demonstrate aggressive behavior is the best way to pick the right dog for you. 

Read on to find out which breeds are generally the most aggressive. We’ve separated the dogs into small, medium, and large breeds so you can go right to the size you prefer.

Known for being fearless and self-confident, a German Shepherd will assertively stand its ground and makes a great watchdog.

How is Aggressive Behavior Measured?

Many tests exist to measure how aggressive a dog is. Organizations such as the American Temperament Test Society offer tests for aggressive tendencies and also keep some statistics on a few different breeds. The ATTS says its test attempts to measure shyness, friendliness, aggressiveness, and mood stability.

They also try to find signs of the dog’s predisposition toward self-preservation and protection of its owner/family. By creating a walkthrough test that creates similar conditions to a regular walk through a neighborhood or park, the researchers can see how the dog behaves. Different breeds also have inherent aggressive qualities. 

What Are the Most Dangerous Dog Breeds?

American pit bull terriers are renowned for their aggressive tendencies. Stereotypes about dogfighting with pit bulls haven’t helped their image for people who are looking for a family-friendly dog, but with consistent training, some have found that pit bulls are fine pets under the right circumstances. 

Other breeds like Rottweilers and bullmastiffs are also infamous for displays of aggressive behaviors and dog bites. Even the much-beloved German shepherd can lash out at times. However, situations and the training of the individual dog all come into play. For most of the dogs on our list, there are certain times when they might be the right pet for some people. 

Top 10 Most Aggressive Breeds of Small Dogs

They might not look like much, but suffer a bite from one of these little animals and you’ll certainly still feel it. Plus, many of them can make up for their lack of physical stature with loud barking and other irritating behavior. If that’s a dealbreaker, try to avoid these 10 breeds of dog when you’re trying to find your next pet:

1. Chihuahua

These little dogs are one of the most popular for apartment-dwelling owners.

Photo: Rover

Because of their incredibly small size, chihuahuas can become aggressive from an early age. Their bark is louder than their bite, but they’re overprotective of their owners, and just about anything might set them off. With consistent training, chihuahuas can be great dogs. But if you’re a sucker for small animals, you might find that this small breed will take advantage and try to act like the lord of the manor.

2. Pekingese

Similar to chihuahuas, Pekingese are tiny dogs who are very protective of their owners.

Photo: BarkPost

Put them in a small home with a few people who they can familiarize themselves with from a young age and Pekingese do great. If you have small children who might approach with abandon, Pekingese might not be the best choice until the kids are a bit older. If you have time to take the Pekingese on a brisk walk, it will burn off most of its excess energy and remain in a calmer mood throughout the day.

3. Dachshunds

Although they seem like little more than adorably stretched-out puppies, dachshunds were bred to have a high prey drive and root vermin out of low bushes.

Photo: LoveYourDog

As such, they still retain the instinct to chase and defend themselves against other animals.

They make great watchdogs and companions for individual dog owners, but they can display aggressive behavior against people they’re unfamiliar with. That being said, they’re incredibly loyal dogs. If you’re looking for a family pet, the dachshund isn’t for you – they’re not great with small children.

4. Poodles

The poodle was bred by Germans and the French to be working dogs, accompanying their owners on hunting trips where they would retrieve targets.

Photo: CentralParkPuppies

They’re regular winners and dog shows and have a very high level of intelligence. Poodles are great lap dogs when they’re sleepy but once they get bored they spring to life and try to find something to occupy their sharp minds. That restlessness can often lead to barking and aggressive behavior.

5. Jack Russell Terrier

Yet another small dog with a high prey drive, Jack Russell terriers were bred to be working dogs on farms.

Photo: LoveYourDog

They also search for constant activity and have a seemingly inexhaustible energy supply. Their comparatively longer legs allow for them to run more easily and that’s what they love to do. If you don’t have much space for a Jack Russell terrier to run great distances and wear itself out, you’re more likely to see some aggressive behavior out of it.

6. Shiba Inu

Hailing from Japan, the Shiba Inu tends to have light orange fur that is much cleaner and more shapely than other dog breeds.

Photo: K9 Web

They’re very independent dogs that like to have their downtime and may be able to take down much larger breeds. Probably the most problematic thing about this breed is its high-pitched wail. Give them enough space to do their thing and hopefully, you can avoid their trademark whining.

7. Pomeranian

A goofier crossover of poodles and the Shiba Inu, Pomeranians are friendly with known people.

Photo: DailyPaws

However, their sensitivity to unfamiliar stimuli can make them hard to socialize properly. Once they’re outside the new puppy phase, they’ll get spooked by the smallest noise and start barking noisily. Their size is just right for a small apartment but be ready for them to bark anytime a truck drives by, there’s a knock at the door, or a moth lands on the wall.

8. Miniature Chow Chow

These downsized versions of the larger Chow Chow are the teddy bears of small dogs.

Photo: The Happy Puppy Site

Many people seek them out as a family pet that they can buy as a new puppy and raise alongside small children. Mini chow chows are very protective and territorial. They can also be quite stubborn and difficult to train for that reason. The mini Chow Chow may also face health issues depending on how the breeder was able to make the miniature version.

9. Boston Terrier

Americans love this bug-eyed small dog. They take quickly to training and are incredibly friendly toward their owners.

Photo: The Little Pet House

However, they may also attempt to scare away strangers and smaller animals to protect their owners. If you plan to have them living alongside other pets, early socialization is the only way to prevent them from barking eternally. As a purebred breed, Boston terriers can also face breathing issues and other health issues such as cataracts or deafness.

10. Shi Tzu

Another very popular breed, Shi Tzus often endear themselves with their flowing fur and small underbite.

Photo: NomNomNow

By the time owners realize how high-maintenance this breed is, they already have the pet home with them. Keeping that fur clean is just one part of Shi Tzu’s needs. They bite regularly if they don’t have proper socialization from an early age. However, if you get the training right and have a nice quiet environment for them to live in, the Shi Tzu can be a great companion.

Top 10 Most Aggressive Breeds of Mid-Sized Dogs

Some of the most popular breeds are medium-sized. If you don’t have much experience with dog training, you might want to stick with a calm labrador retriever rather than one of these 10 more aggressive breeds. 

1. Bull Terrier

Straddling the line between small dogs and medium-sized ones, bull terriers are especially muscular for their size. They can become rather aggressive without the proper training. That being said, if they have the right environment to live in they can be great family dogs. Just make sure you have experience training and handling a pet before you jump into bull terrier ownership since they can be a lot to handle.

Photo: The Happy Puppy Site

2. American Bulldogs

Though they can be perfect family pets with the proper training, American Bulldogs can turn into aggressive nightmares if they aren’t properly socialized and trained from an early age. Like smaller dogs, the Bulldog can get mean to compensate for its size if it isn’t familiar with other dogs. Plus, they’re a bit slow and less aerodynamic than other breeds, so they tend to stand still and bark to get their point across.

Photo: EBKC

3. Boxers

Boxers are chock-full of energy and they can show aggressive behavior if they don’t burn off that fuel regularly.

Photo: Love Your Dog

If they have space to run and play, then they’re usually great, calm pets. They can also fear strangers, even small children if they don’t have a history of socialization. This breed has a history as a hunting dog and has lots of strength, which can be bad if it’s not properly trained. 

4. Blue Heelers

Also called the Australian Cattle Dog, Blue Heelers are natural herders.

Photo: Dogs Love to Know

That’s great for farm work, but it’s not a strange sight to see them trying to herd groups of people or even small children. Unfortunately, the main method these herders use is a nip at the ankles. If you can train that out of them, Blue Heelers are very smart and alert companions.

5. Border Collies

Similar to Blue Heelers, Border Collies are herders, albeit less severe than their Australian counterparts.

Photo: Lucy Pet Products

Border Collies are one of the most popular breeds around, but they’re also athletic and tend to get anxious and act out if they don’t have the space to exercise and play. 

6. Dalmatian

These distinctive breeds are great hunters and herders.

Photo: K9 Web

They can be trained to do some amazing things, but they’re also territorial and tend to be more reserved when there are other dogs around. Some have found success with the early socialization of their Dalmatians. With proper training, Dalmatians are also some of the best possible watchdog breeds.

7. Beagle

Energetic hunters and herding dogs with uncanny senses of smell, Beagles are extremely single-minded when it comes to new scents.

Photo: Mental Floss

They also howl like crazy. Though they mostly have a friendly nature, the beagle can also become very aggressive when it has a target or if it hasn’t had socialization from early on in its life.

8. Doberman Pinscher

These dogs can range from medium to large-sized.

Photo: Wikipedia

Because they can be trained to attack only when provoked, Doberman Pinschers make great guard dogs. However, they tend to only recognize people they see regularly like family members or fellow pets. They’re great dogs for expert owners and trainers, but first-time or casual dog owners should avoid this particular breed.

9. American Staffordshire Terrier

Frequently confused for pit bulls, the American Staffordshire Terrier also has a dogfighting past but makes a great family dog with the proper training.

Photo: LoveYourDog

Early socialization is key for them. They train much better when they live inside with the owner and other family members. Amstaffs also like to escape, so if you don’t have adequate fencing you could run into trouble with your insurance company or worse.

10. Akita Inu

A larger version of the similarly-named Shiba Inu, Akitas are gorgeous but also have a high prey drive and are more dominant than other breeds.

Photo: Reddit

Family members and others the dog regularly sees are probably fine, but for new dogs and other strangers the Akita Inu may act out. 

10 Most Aggressive Breeds of Large Dogs

Aggressive behavior is always scary from a dog, but it’s even more alarming coming from one of these large dog breeds. 

1. Presa Canario

Aggression from Presa Canarios is almost always based on their guard dog instinct.

Photo: Wikipedia

They start to decide who they should protect and may lash out at strangers and other dogs that they perceive as a threat to their master or other family members in the same household. If you have plenty of space and no neighbors, this is a great dog to have. But if you can’t be forceful with training and the Presa Canario will run into lots of different people, you’re probably better off with another breed. 

2. Mastiff

Mastiff puppies are cute and playful, so by the time owners realize a lack of training and early socialization has turned their mastiff into an aggressive dog, it could be too late to change course.

Photo: Love Your Dog

Limit biting with firm and accessible commands from early on and a mastiff can be a great dog.

3. Cane Corso

The Cane Corso looks like it could have been a dogfighting champion, but it doesn’t share that background with pit bulls.

Photo: The Spruce Pets

While they are very protective of their owners, they’re also one of the most trainable dog breeds out there. Cane Corsos do need lots of attention to limit their destructive behavior, but if you can train and pay attention to them then aggression from Cane Corsos can be kept to a minimum.

4. Alaskan Malamute

These snow dogs like to be the leader of the pack and they only tend to listen to people who can give that impression during training.

Photo: BarkPost

They can be trained to obey commands, but Malamutes rarely make good companions for other animals. Even other Malamutes are a risk. They have food aggression and require constant training to remain unproblematic. 

5. Pit Bulls

Though many are friendly, pit bulls were bred for dogfighting, and that aggressive behavior is likely to surface without the proper training.

Photo: RD

Most purebred pits rarely lash out at humans if they’ve had proper training throughout their life, but mixed breeds can still be dangerous for both people and animals. Insurance companies are notoriously anti-pit-bull, so do your research before you start shopping around for one.

6. Rottweilers

These big black dogs tend to lash out when they feel they need to go on the defensive.

Photo: Wikipedia

That can be to defend food or it might be to protect their owners or other members of the household. If the aggression is countered via early training, you’re much more likely to have a calm pet in a rottweiler. 

7. German Shepherds

Famously common as police dogs, German shepherds need owners who know how to train them from early on and how they behave later in life.

Photo: Jakobagsds

Otherwise, their concern with territory and guarding could cause them to lash out at other animals or people. 

8. Great Danes

A well-known dog species, the sheer size of many Great Danes makes them fearsome if they’re displaying signs of aggression.

Photo: Great Dane Care

Thankfully, they’re unlikely to bite. But Great Danes can still be aggressive if they’re kept cooped up inside or go without proper training. 

9. Siberian Huskies

Unlike some of the other big dogs in this guide, Siberian Huskies aren’t typically thought of as an aggressive breed.

Photo: Highland Canine

But they need lots of attention and exercise to stay on their best behavior. Leave them cooped up in a house or a small yard all day and your Siberian Husky could turn into a troublemaker. 

10. Boerboel

These big dogs are still used as guard dogs on South African farms to this day.

Photo: Wikipedia

Their huge size helps them ward off big predators like lions. They’re very loyal, but like many other big dogs, these need significant amounts of training. Outside of a farm environment, a Boerboel could treat everyone entering your house as an intruder and give them a loud unwelcoming greeting. 

Conclusion:

Overly aggressive behavior is the worst thing a dog can display. No matter how much you love your dog, if it lashes out at others you could be finding yourself having to get rid of it. It’s not only the Pit Bulls and Rottweilers that can be aggressive. Without the right environment and training, any of the thirty dogs in this list may turn into monsters. Be on the lookout for the aggressive dog breeds in this guide as you look for your next pet.