The Tibetan Mastiff is a powerful, heavy, but athletic dog, the Tibetan Mastiff is built to combine strength and agility. Its body is slightly longer than tall. Its walk is slow and deliberate, while its trot is powerful and light-footed. The whole appearance is impressive, with a solemn but kindly expression. The coat, which is noticeably heavier in males than in females, is thick and fairly long, especially around the neck and shoulders. The tail is densely coated and the hind legs well feathered on the upper parts. The hair is coarse, straight and hard, standing off from the body. It carries a heavy undercoat in cold weather, but little undercoat in warm weather. This combination of coat types allows the Tibetan Mastiff to endure the extremes of Tibetan weather.

As befitting their long past as a solitary sentry and protector, Tibetan Mastiffs are independent, strong willed, and territorial. They are aloof toward strangers but devoted to their family. Proper socialization is essential so that they will accept strangers and not become overly suspicious. They are gentle and patient with their children, but may guard their home against visiting children who may appear to be threatening the family children. They are generally good with other dogs and are rarely dog aggressive. (In Tibet, they were often kept with Lhasa Apsos.) Most Tibetan Mastiffs are good with other animals.