The Tosa Inu or Japanese Mastiff is the cousin to the Korean Mastiff also known as the Dosa Inu with the Tosa Inu however tending to be smaller and less mastiff looking in appearance.
As with many show dogs the show ring, judge bias and registry politics have created situations where breeders have upbred this breed. For this reason those bred outside Japan are often much larger than those still being bred in Japan. In some cases those outside Japan have nearly double the size of their native counterparts.
The breed is believed to have been derived from the native Shikoku-Inu and then crossed with European dog breeds, such as the Old English Bulldog in 1872, Mastiff in 1874, St. Bernard, German Pointer in 1876, Great Dane in 1924, and the Bull Terrier.
During 1924-1933 the breed had its greatest demand in Japan with over 5,000 breeders. Since then the breed however has faced significant decline.
Like many of the mastiff breed lines this breed also faces limitation in ownership through breed specific legislation (BSL) and is only allowed in the UK under exemption through the British court, Australia prohibits their import, and they are significantly regulated in Trinidad and Tobago. The breed is also banned in Cyprus, Denmark, Hongkong, Iceland, Malaysia, Malta, New Zealand, Norway, Singapore and Turkey.