The Bullmastiff is a powerful dog, said to be a cross between the Mastiff and the Bulldog. Originally bred to find and immobilize poachers, the breed has proved its value as a family pet. Large, by family standards, the dog weighs 115 to 135 lb (52 to 61 kg), at 30 inches (762 mm) tall, with the bitch 20 to 30 lb (10 to 15 kg) lighter and 3 inches (76 mm) shorter. They make good parents, and often produce more than six puppies in a litter.

Bullmastiffs come in a few different color varieties: fawn, apricot, and brindle. The fawn is a light tan color, while the apricot is a richer, reddish brown. Brindle bullmastiffs range in colors and markings, depending on the coloring of the parents. The brindle markings appear as a mottled striped look, with a mixture of the fawn or apricot coloring and darker or black markings. All of the varieties of bullmastiffs have a dark mask on their face.

With its handsome, powerful appearance and superb speed coupled with strength and endurance it can overtake and capture intruders without mauling them. These traits make the Bullmastiff appear to be an excellent choice for a guard dog; however, a stubborn streak makes the animal resistant to obedience training and overly protective of its human family. Due to this, the breed has been overtaken by others, more popular as guard dogs.

This dog was popularized by the media in Canada in the late 1990s as being the breed of dog in a string of (unrelated) dog attacks against children. The proposal to ban the breed in Canada started a small movement that ultimately failed.