Tosa Inu

Stuart Fitzgerald
Dr Stuart Fitzgerald (MVB MANZCVS, University College Dublin)
Photo of adult Tosa Inu

The Tosa-Inu, also called the Japanese Mastiff, is a breed of fighting dog that was developed in Japan from the mid-nineteenth century. Outside Japan, the Tosa was crossbred with large and giant breeds, including the Great Dane and Mastiff, to produce very large individuals, while those bred in Japan remain truer to the original type, at around half the size. The breed is considered “dangerous” in many jurisdictions, and ownership in the UK and Ireland is strictly controlled and subject to license. In the right environment, with firm discipline and a confident owner, a Tosa can be a placid, easy-going giant. However, aggression toward other animals is a significant problem, and aggression toward strangers can also be an issue without adequate socialisation and training.

The breed is not recommended for families with children or other pets, and ownership comes at a large cost, both financially and in terms of responsibility. Tosas need regular intense exercise to stave off boredom and frustration, and enjoy activities, such as cart-pulling, which provide more vigorous exercise than simply lead walking or running. Being a mastiff breed, the Tosa-Inu is known to be a heavy drooler, and its large bulk means that it is not an ideal indoor-only dog. The breed is generally very healthy, with a life expectancy of 10–12 years.

About & History

Dog fighting has long been a popular pursuit in Japan, and it still is today, particularly in rural areas, where tournaments are often organised and supported by the yakuza, the Japanese mafia. Dogs involved in these events must be fearless, aggressive, and powerful, and these traits may be seen in the Tosa-Inu, which is still the dog of choice for these fights. Participants are frequently seriously injured or killed, and animal rights groups are actively campaigning for the banning of this “sport”. The breed was developed from molosser dogs, which were large mastiffs used throughout Asia and Europe for centuries as warriors and guard dogs. The modern Japanese form of the breed was established around the mid-1800s.

Dogs exported from Japan to Europe from this point in time were bred with a succession of larger breeds, from the Bulldog and Mastiff to the Great Dane, to produce a western variety of the breed that is significantly larger and more imposing than its Japanese parent stock. The breed has never attracted a large following outside of its homeland, where thousands of litters were being bred annually in the mid-twentieth century. Part of the reason for this is the potential for behavioural problems and attacks on animals and humans, which has led to the introduction of either bans or strict controls on Tosa ownership in many countries.

In the UK, ownership or import of Tosa-Inus requires a legal exemption issued by a court, while in Ireland, the breed has been banned from public housing projects, and is considered dangerous. The Tosa is not officially recognised by either the UK or American Kennel Clubs, and the breed standard in general use is that issued by the Federation Cynologique Internationale.


Tosa Inu Large Photo

The Tosa is a massive dog that carries itself with dignity, in the manner of the Great Dane used in its development. It has a strong, broad skull with heavy temporal muscling, and a pronounced stop leading to a powerful, square muzzle. The jaws and teeth are very well developed, and it is important the breed has a perfect scissor bite with no hint of an overbite. The ears are quite small and thin, and hang close to the side of the face, where they are set high. The eyes are a dark brown in colour, are quite small, and usually convey a serene expression.

Every part of the Tosa is heavily-muscled, and this is particularly pronounced in the neck, which has a broad muscular arch, and a dewlap of redundant skin, which is useful to the dog when fighting, so as to allow it to turn on its attacker even while being held. The high withers lead to a wide, straight back and loins, and even the base of the tail is massively muscled. The chest is moderately well sprung, and is deep, which causes the abdomen to be sharply tucked.

The limbs are well angulated, which allows for athleticism and the maximum return on muscular effort. The breed has strong, heavy boning, and tight paws with well developed pads. The Tosa has a short coat of hard, coarse hair. Several colours are commonly seen:

  • Red
  • Fawn
  • Apricot
  • Black
  • Brindle

Small white patches sometimes develop on the chest and feet, but these markings are not encouraged by the breed standard. Male Tosas stand between 60–65 cm (24–26 in) tall at the withers, and females average 55–58 cm (22–23 in). The weight range for both sexes is anywhere from 38–60 kg (84–132 lb), depending on their build and familial characteristics.

Character & Temperament

A well-adjusted Tosa-Inu is calm, laid back and immensely loyal to its owners. With sufficient exercise, most individuals will spend large parts of the day relaxing around the home. However, they are also often suspicious and resentful of strangers, and are quick to respond with aggression to any perceived threat. Without adequate socialisation, this aggression can be difficult to handle and redirect, creating a viscous circle in which owners limit their dog’s contact with other people for fear of putting them at risk.

Many Tosas have a high prey drive, and will pursue wildlife and smaller pets, including other dogs. For this reason, they are best kept as the only pet in most homes. In the hands of an inexperienced handlers, the breed tends to be overly assertive, and may resent weak efforts by the owner to control it. However, Tosas respect a strong pack leader, and will become very devoted to those they recognise as being in charge. For this reason, it is vital to implement an obvious and well-defined pack structure from a very young age.


Photo of Tosa Inu puppy

Tosa-Inus are bright, but stubborn, dogs. Most have very clear ideas about how they would like to behave, and it can take a great deal of effort to make them come around to their owner’s way of thinking. Good behaviour and high levels of obedience training are mandatory for such a large and potentially dangerous breed, and so owners must be prepared to put in the work required to achieve these goals. The assistance of a professional dog trainer can be invaluable, especially when beginning to train a young Tosa.

For puppies, the priority is thorough socialisation, particularly with people. Inviting friends and extended family to spend time with the pup, taking them for walks, and offering treats and praise, is a great way to introduce the young dog to strangers, by providing positive experiences at each interaction. Though socialisation with other dogs is also valuable, the breed can rarely be trusted with its own kind, and so the returns on time invested in dog-to-dog interactions may be more limited. Because of the breed’s size and strength, innocent competitive games, for example, tug-of-war, should be avoided so as not to encourage competition between dog and owner.


The world of dog fighting is an unforgiving one, and the selective breeding necessary to produce competitive dogs, combined with more recent cross-breeding in the West, has produced a breed with few significant health problems.

Allergic Skin Disease

Tosas are prone to allergic skin disorders, which may be caused by a range of allergens, from dust mites to food constituents. Typical signs of allergies include reddening and irritation of the ears, face, paws, and perineum, which may progress to secondary skin infection, hair loss, and scabbing. Identification of causative allergens is difficult, but may involve skin scrapings and food and medication trials.

Behavioural Disorders

As outlined above, the Tosa has a strong personality, and a tendency to aggressive behaviour. In the wrong hands, this aggression can be very difficult to manage, and many dogs are surrendered each year for this reason. This is best prevented through early socialisation and training, as rehabilitation of a large, aggressive adult Tosa is fraught with difficulty.

Elbow Dysplasia

Developmental disorders of the elbow joints are common in many large breeds, including the Tosa-Inu. Signs often manifest as early as five months of age, when abnormal growth in one or more areas of the joint cause pain and lameness. Because of the innate high pain threshold of the breed, signs may not be noticed until adulthood, when irreversible arthritic change is likely to have occurred.

Hip Dysplasia

This condition shares many characteristics with elbow dysplasia, in that it may first be noticed in younger dogs, and the resulting joint incongruity eventually leads to osteoarthritis of the hip joint. Both elbow and hip dysplasia have a strong genetic component, and hip and elbow scoring schemes have long been in operation to remove affected adults from the breeding stock. Anyone considering the purchase of a Tosa should insist on seeing scoring certificates from both parents.


This is a usually benign condition seen in several of the large Japanese breeds. If asymptomatic, it may be detected as elevated blood potassium levels on routine blood screening, something which is exacerbated by eating onions or garlic. If severely affected, lethargy and cardiac arrhythmias may be noticed; however, these are unusual findings.


An underactive thyroid gland is a relatively common cause of weight gain and hair loss in the breed. Dermatological signs can overlap with those of allergies, as discussed above, and so investigation of either condition will often involve blood tests to examine thyroid hormone levels.

Exercise and Activity Levels

Though happy to spend large amounts of time relaxing, Tosa-Inus do need a good deal of daily exercise. Between one and two hours should be allotted daily for walking or jogging, as well as providing access to a secure outdoor garden or yard. Ideally, Tosas should be given more vigorous exercise, for example, pulling a cart, or can be provided with a weighted doggy backpack while out walking. Such exercise aids will give the dog more satisfaction from its daily activities, and reduce the likelihood of aggressive or other undesirable behaviours.


Because the breed’s coat is short and coarse, it does not generally require any special care. Weekly brushing will help to keep the skin and hair in good condition, and occasional bathing may be necessary to help remove any more tenacious dirt and to deodorise. Tosas shed a small amount year-round, and also drool quite a bit, though not as heavily as some other mastiffs. For these reasons, it requires more effort to maintain a Tosa’s home than to groom the dog himself, and keeping packs of baby wipes around the home is a useful way to manage the inevitable pools of slobber before they dry into furniture and carpets.

Tosa-Inus have very strong nails, which are usually dark. Keeping these trimmed is important to prevent them growing into the pads. This requires a strong set of nail clippers, and the habit of nail trimming should be introduced to pups at a young age so it is not resented later in life. With dark nails, it is not possible to visualise the sensitive quick within, and so small, regular trims are preferable to taking larger chunks less frequently, when the risk of hitting this vascular structure increases.

Famous Tosa Inus

In Japan, celebrity status is awarded to those Tosas that are victorious in the dog-fighting ring, with the most successful being bestowed the title of “Yokozuna”, a moniker also used in the world of sumo wrestling. These canine sumos are also adorned with decorated cloth and braided rope, as are their human counterparts.


Because of their tightly regulated status and rarity outside of Japan, it is very unusual to find Tosa hybrids for sale in the UK or Ireland. Those that are crossed are often mixed with other dogs considered potentially dangerous, such as the Presa Canario, Fila Brasileiro, or Dogo Argentino.

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