Get

In Your Inbox

Dogster is reader-supported. When you buy via links on our site, we may earn an affiliate commission at no cost to you. Learn more.

How Aggressive Are Mastiffs? Breed Facts & Prevention Tips

Share

English Mastiff Closeup

Mastiffs have a reputation for being aggressive and even scary. Many people actively avoid these dogs for this reason, and they’re such big animals that you can’t really blame those who are wary of them. But exactly how aggressive are Mastiffs?

Most Mastiffs are not aggressive and are actually lumpy couch potatoes. But not all of them are. Here is what you need to know about this breed’s history, Mastiff aggression and why it’s so feared, and how to prevent your dog from being aggressive.

divider dog paws oct 2024

Are Mastiffs Aggressive?

Some facets of society, like local governments, landlords, and insurance companies, have labeled the Mastiff as an aggressive breed. They have a higher-than-average chance of exhibiting aggressive behavior. Obviously, not all Mastiffs are aggressive. Some are the sweetest dogs in the world, but others can be quite anxious and adverse to strangers.

One reason that a Mastiff’s aggression is so feared is that their immense size and power can make them incredibly dangerous if they are not handled properly. The potential for violence is what makes local governments and insurance agents so cautious about this breed.

Portrait of a Mastiff Dog in outdoors
Image Credit: Ricantimages, Shutterstock

How Aggressive Are Mastiffs?

Mastiffs are not hyper-aggressive dogs. When they are at rest and not anxious, they are sweet and relatively lazy. They are not going to be up and moving around, patrolling your house for signs of danger. They can often be found lying on the couch, listening for something out of the ordinary. They can be wary of strangers and excellent guard dogs in that they will alert you when someone or something is coming. They are not attack dogs, though, and they are not on alert 24/7.

Some Mastiffs are more aggressive than others. The differences are often found in the way that they are socialized and trained. Some people feel safe with a protective dog and will encourage behaviors that can be seen as aggressive. Other people enjoy Mastiffs for their size and cuddly loyalty but want nothing to do with possible aggression. A dog that is trained and encouraged to be protective will always be more aggressive than a dog that is well-socialized and rewarded for being sweet and lazy. Mastiffs can be both of these things, and the trouble is that you cannot know at first glance which type you are dealing with.

divider dog paws oct 2024

What Were Mastiffs Bred For?

The Mastiff is an ancient breed with roots going back as far as the Roman Empire. They were bred and transported throughout the empire, making it as far north as the British Isles. They were prized for their size, strength, and power. Many were bred as protectors and guard dogs. Before the rise of Ring doorbell cameras, people could only rely on their own senses and those of their dogs to alert them to danger and help protect them. Mastiffs were often found on farms, in Roman-style compounds, and in manors as companions and protectors.

Since then, Mastiffs have continued to be prized for their size, loyalty, and protective nature. The modern age does not require people to rely on guard dogs as much as they had to in the past, so there are more socialized and friendly Mastiffs than before, but generations of protective breeding and training are still present.

Spanish Mastiffs
Image Credit: Marcelino Pozo Ruiz, Shutterstock

Mastiffs Can Be Dangerous

The crux of the issue is that while most Mastiffs are perfectly calm and safe, they have the potential to be incredibly dangerous. They can grow to absolutely immense sizes. Adult male Mastiffs can stand over 2 feet tall and weigh as much as 230 pounds, which is more than most adult humans. Even the females typically weigh at least 120 pounds on the small end. They are one of the largest breeds in the world by a long shot. It only takes a Mastiff getting out of hand for a second to scare or injure someone. Their large size makes them especially dangerous to children who are small and do not have the knowledge to know when a dog is starting to feel ornery or aggressive.

The Mastiff was the sixth deadliest dog in the United States according to stats compiled between 2005 and 2017, with 14 deaths attributed to Mastiff attacks. That is far below the top dogs, Pit Bulls and Rottweilers (284 and 45 deaths, respectively), but it is still not zero. The size and power of this breed gives them ample potential to seriously hurt someone.

How to Prevent a Mastiff From Being Aggressive

The absolute best way to prevent a Mastiff from being aggressive is to prioritize socialization and training from a young age. Calm behaviors should be rewarded and aggressive behaviors should be ignored. Dogs like Mastiffs should never be subjected to negative reinforcement training or fear training (yelling, striking, shock collars, etc.), as these can actually create more anxiety and aggression.

Socializing a Mastiff means introducing them to a variety of different people, locations, and animals. A dog that is kept at home all the time with the same people around will naturally be curious or wary of the odd stranger that comes by once in a blue moon. A dog that gets out of the house and sees new people regularly or even takes long, diverse walks will have more information and experiences that will help them deal with situations in a healthy and calm manner.

Training and socialization are the two pillars of reducing the potential for aggression in any dog. Similarly, some people purposefully do not socialize their dogs and encourage aggressive behaviors to cultivate stronger and more fearsome guard dogs or protectors.

Blond boy with a large dog, English Mastiff
Image Credit: Vira Sivachuk, Shutterstock

divider dog paws oct 2024

Conclusion

Mastiffs are generally not aggressive. Many people think that this breed is always on alert and ready to strike, but that is simply not the case. Their reputation comes from the fact that they can be aggressive, and their massive size makes any moments of aggression potentially dangerous. Most Mastiffs are sweet and lazy and have no issues with strangers at all, but some are anxious and do not do well around strangers, and that is what people zero in on.


Featured Image Credit: Mikanah, Shutterstock

Want content like this delivered to you?

Sign Up For Our Newsletter

News, insights, expert advice, and everything dog

* By submitting, you agree to our Terms & Conditions and Privacy & Cookies Policy.




How useful was this post?

Click on a star to rate (you can leave written feedback after clicking submit)

Help us improve Dogster for pet parents!

Your feedback really matters.

What did you like about this post? Also how can we improve it?

Join the conversation

Leave a Reply

You’re very welcome to leave a comment or question. Please know that all comments must meet our community guidelines, and your email address will NOT be published. Let’s have a positive and constructive conversation.


Talk With A Vet Online

Peace of mind,
anywhere, anytime

Affordable vet advice

Ask Dr. Paola- Help! My Dog’s Sleeping Habits Have Changed! (May 18, 2026)

Welcome to our “Ask Dr. Paola” series, where every Monday we bring expert advice straight from Dr. Paola Cuevas (MVZ) to help our...

The Crate Setup Most Dog Owners Get Wrong (And How To Fix It!)

Most people assume that if their dog hates the crate, the crate is the problem. So they try a bigger one, a different...

1,500 Beagles Rescued from Wisconsin Lab Farm – Here’s Where They’re Going

You may remember that a few weeks ago, we reported on a tense situation at Ridglan Farms, Wisconsin, a facility infamous for housing...

Dogster’s Weekly Photo Contest Winners: Window Watchers (May 11, 2026)

Every week our team gets the privilege of sorting through our readers photos to choose what dogs will win this weeks contest! See...

More related

How Many Ribs Do Dogs Have? Vet-Approved Anatomy Facts & Info

The rib cage of a dog serves the function of protecting the internal chest organs, particularly the lungs and heart. That speaks to...

160 Awesome Maltipoo Names: Fun & Cute Options for Your Dog

The Maltipoo is a mix of two adorable breeds: the Maltese and the Poodle. These fluffy dogs are full of personality and love,...

20 Unique Haiku Poems About Dogs

Haikus are short, to-the-point poetry pieces that are easy to read and write. Whether you’re looking to read some short and sweet haikus...

Bulldog Dog Breed: Info, Pictures, Care & More

Bulldogs, with their unmistakable wrinkled face, sturdy build, and unique charm, have captured the hearts of dog lovers worldwide. Originating from England, Bulldogs...

Keep reading

Can Dogs Eat Alfredo Sauce? Vet Reviewed Nutrition Facts

Alfredo sauce is an Italian sauce made with cheese, butter, cream, and salt, but typically also includes garlic and onion. Dogs do not need to be given extra salt in their diets, and even if your dog can tolerate dairy...

Can Dogs Eat Alfredo Sauce

Can Dogs Eat Marshmallows? Vet-Verified Risks & FAQ

We all love to indulge in a treat from time to time, and marshmallows are as indulgent as they come. Roasted over an open flame or mixed in with Rice Krispies, they are delicious and super-sugary snacks. But is it...

Can Dogs Eat Marshmallows

Menadione in Dog Food: Vet-Reviewed Safety Facts

We all want to feed our dogs the best type of food we can. With such a plethora of choices on the market coupled with never-ending advice and opinions on which diet is best, what ingredients to avoid, and which...

Italian Greyhound dog eating from bowl at home

Can Dogs Eat Hemp Seeds? Vet-Verified Facts & FAQ

There are many highly nutritious superfoods on the market that we add to our diets daily, and we may consider doing the same for our dogs. Hemp seeds are a popular human superfood, and hemp-based products are now thriving in...

Can Dogs Eat_Hemp Seeds

Can Dogs Eat Saffron Rice? Vet-Verified Facts & Safety Guide

Saffron rice is a tasty and savory dish, and dogs may be tempted to eat it. Many dogs enjoy the taste of rice and may see no problem with eating saffron rice. However, the issue with saffron rice is that...

Can Dogs Eat Saffron Rice

Can I Claim Dog Food on My Taxes in 2026? Pet-Related Deductions Guide

Tax season is never fun. We always hope there are things we can claim when filing. Surprisingly enough, there are several cases where the cost of your dog’s food may be tax-deductible. Usually, pet-related expenses are considered personal expenses, so...

woman computing taxes with her dog

Purina Pro Plan Dog Food Review 2026: Pros & Cons and Recalls

Review Summary Purina has been one of the top producers in the pet food industry for over 90 years and has been a trusted brand for just as long. Since it has such a large variety of brands and recipes,...

Dogster_Purina Pro Plan Dog Food Review

Can Dogs Have Cumin? Vet-Reviewed Nutrition Facts & FAQ

When you think about giving your dog a bite of your food as a treat, you probably don’t think about what spices the food contains. You should, though, as some spices are toxic to our canine companions, so even a...

Dogster-Can-Dogs-Have-Cumin

Love Dogs? So Do We! Join the Dogster Community

Stay informed with expert pet care insights delivered straight to your inbox! Discover professional guidance on animal behavior, feeding tips, trusted product picks, and much more.




Sign up for the Dogster Email Newsletter