Top 10 Most Aggressive Dog Breeds: You Won't Believe #1

Much as we love our four-legged canine friends, it's important to remember that they are still animals, and like any other animal, they have the capacity to become aggressive. Dogs are the descendants of wolves, any many popular breeds that we keep as house pets today were originally bred for violent or dangerous work like hunting, guarding, and sadly, in some cases, even dogfighting. While there are a lot of factors that determine whether or not a dog may have a predisposition to aggressive or unpredictable behavior, genetics does have an undeniable influence.

We checked numerous studies and statistics to determine which breeds were the most aggressive, and these 10 were among the most frequently named ones that we found. Before we share our list of the most aggressive dog breeds, however, we wanted to give a couple of caveats first.

Things To Keep in Mind

Before we start talking about which dog breeds may have a higher capacity for aggression, it's absolutely crucial to remember that breed is not the biggest determiner of a dog's behavior. The AAAS states that environment (which includes how a dog is treated and how it's been socialized to other humans and pets) has far, far more to do with a dog's behavior than their breed. To put it simply, nurture is more influential than nature.

There are other mitigating factors that can determine how aggressive certain dogs are likely to be. A 2021 study from the University of Helsinki found that older dogs tended to be more aggressive than younger ones; males are more aggressive than females; fearful dogs and dogs suffering from painful medical conditions were more likely to lash out; and, funnily enough, small dogs were more likely to be meaner than medium- or large-sized dogs!

Finally, certain dog breeds are more likely to be perceived as aggressive by the public, which can lead to negative biases, over-reporting of aggressive behavior, and unreliable anecdotes about them. Furthermore, dog breeds that have an aggressive reputation are often chosen by people who intentionally enable that aggressive behavior, and it becomes a sort of sad, self-fulfilling prophecy.

All this is to say that no dog is born "bad," and there's much, much more to a dog than their genetic background. Still, because certain breeds do tend to have at least some potential for higher aggression than others, it's important to know which ones to be more wary of, especially if you're thinking of adopting a dog.

The Most Aggressive Dog Breeds

1. Rough Collie

Hold on - record scratch - WHAT? Surely not Lassie! We had a hard time believing that ourselves, but there's science to back it up. The aforementioned study from the University of Helsinki studied the behavior of thousands of dogs from roughly two dozen breeds, and the Rough Collie topped their list of breeds with the highest probability of aggressive behavior. The American Temperament Test Society (ATTS) also lists the temperament testing pass rate for Collies at 80.79% lower than the average overall pass rate of 83.4%.

2. Chihuahua

We have a feeling this one's less of a surprise than the Rough Collie. Though they may be little, the Chihuahua is fierce, with a widely-held reputation for aggression that's frequently backed by evidence (including the University of Helsinki study). Chihuahuas don't fare too well in ATTS rankings, either, earning only a 68.8% pass rate.

Because of their small "toy breed" size and their popularity as family dogs, many people perceive Chihuahuas as less dangerous that bigger breeds. But while an angry Chihuahua is unlikely to threaten your life, they can be very aggressive towards new people, pets, and kids who don't respect their personal space. However, if you're going to adopt a Chihuahua, early and consistent training and socialization can help mitigate their aggressive instincts.

3. Basenji

The Basenji is a small hound dog breed hailing from central Africa, where they were bred as hunting dogs. Basenji are cute, compact, and unique for their lack of a true "bark" (they have a uniquely-shaped larynx that causes them to "yodel" instead), earning them an almost cultish following among dog lovers.

Unfortunately, they also have a reputation for being fearful, high-energy, temperamental, and prone to aggressive or unpredictable behavior. The Basenji's ATTS pass rate sits at a stark 69.4%, and they're widely considered to be a high-maintenance dog that's not a good fit for first-time parents or households with other small pets. For the right person who's willing to train them and give their dog plenty of exercise, however, a Basenji may be a good fit.

4. Presa Canario

The Presa Canario, also known as the Canary Mastiff, Dogo Canario, or "Presa," is often ranked among the most aggressive dog breeds worldwide. In 2024, they ranked 4th in Canine Journal's list of the most dangerous dog breeds by dog bite statistics. Like other mastiffs, they are large dogs originally bred for hunting, guarding, and bloodsports, and more than 100 fatalities in the US are attributable to Presa Canario attacks.

Here's the good news, though: Presa Canario are intelligent dogs. Though an early training regimen is crucial to inhibit bad behavior, they have the capacity to be very calm, even-tempered dogs, with the breed having an ATTS average pass rate of 90.2%. Even so, Presa Canario aren't recommended for households with small children or pets.

5. Pit Bull Types

The Pit Bull is actually not one distinct breed but an umbrella term encompassing several closely related breeds. Pit Bulls were originally bred for dog fighting, and while they initially had their aggressive instincts towards humans bred out of them, the genetic waters have gotten a little muddy over the years, so to speak. Pit Bulls are often ranked number one in dog bite statistics, which also translates to the highest number of dog bite-related fatalities.

However, it's important to note that these statistics may be affected by 1.) the high prevalence of people with Pit Bulls, 2.) the fact that Pit Bulls are still often mistreated, poorly socialized, or used in dog fighting due to their reputation, and 3.) the fact that Pit Bull bites are more likely to be reported than dog bites by other breeds. In controlled tests, the AVMA has not found Pit Bulls to be disproportionately more dangerous than other dogs. They also have good temperaments, with all four AKC-recognized Pit Bull Breeds scoring above average in ATTS testing. Pit Bulls can be aggressive and dangerous dogs, but with proper training and socialization from an early age, they can be very sweet, loyal dogs, too.

6. German Shepherd

Like Pit Bulls, German Shepherds also rank very highly in dog bite and dog attack fatality statistics. German Shepherds are large, energetic, and powerful dogs with a high tendency towards overprotectiveness and aggression towards strangers. Though they are quite loyal and intelligent and can be very useful as guard dogs and as K-9 police dogs, German Shepherd parents should be vigilant about early training and socialization, and exercise caution when introducing them to children or smaller animals.

7. Rottweiler

According to the MKP Law Group, Rottweilers were ranked 2nd out of the top ten most fatal dog breeds, reportedly contributing to over 10% of all dog attack-related fatalities. Rottweilers are very intelligent and loyal dogs and are even considered sweet-natured by many, but like German Shepherds, they are large, vigilant, and prone to protectiveness, which can turn aggressive if a Rottweiler is not properly trained.

However, this aggression can be easily mitigated with - you guessed it - proper socialization and training. According to the AKC, "a well-bred and properly raised Rottie will be calm and confident, courageous but not unduly aggressive." When raised right, Rottweilers can be wonderful, affectionate companions (and as someone who grew up with a very sweet-hearted Rottweiler as a very young child, I'm partial to them).

8. Huskies

It would be a bit unfair to say that all Huskies are aggressive by nature, because that's not entirely true. In fact, under normal circumstances, they tend to be quite friendly with people. The issue is that Huskies are extremely active dogs that are prone to anxiety and have a high prey drive. Without proper training from an early age and plenty of exercise and mental enrichment, they can become bored, anxious, and temperamental, which can exhibit itself as aggression.

Huskies are not low-maintenance dogs. Any pet parent who's considering adopting a Husky has to be able to put in the time to train them well and make sure their exercise and enrichment needs are met. Additionally, because Huskies have a tendency to chase small animals, they might not be a good fit for households with other small pets.

9. Chow Chow

We're back with another small spitfire! Despite being little and covered with teddy bear-like fluff, Chow Chows were originally bred as guard and hunting dogs, according to PetPlan. They're not "mean-spirited" dogs, but they're strong for their size and tend to be aloof, stubborn, and very wary of strangers. This can lead Chow Chows to be hostile or aggressive towards new people, which is why early socialization is extremely important for their development.

10. Mini Poodle

Once again, a small dog breed makes its big mark. The University of Helsinki study ranked Miniature Poodles (toy, miniature, and medium-sized) as the second most aggressive type of dog, just behind Rough Collies. According to Dietrich Law Firm, Mini Poodles have the strong prey drives of their larger Poodle cousins without an outlet, and they often suffer from "Small Dog Syndrome" (aka a predisposition to anxiety, insecurity, and aggression). As always, though, proper training, socialization, and a healthy outlet for their pent-up energy can go a long way towards raising a calm, even-tempered Mini Poodle instead of a mean one!

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