A kouprey (Bos sauveli, from Khmer: គោព្រៃ Khmer pronunciation: [koː prɨj] 'wild ox', also known as kouproh or grey ox), is a wild, forest-dwelling ox found mainly in northern Cambodia, but also believed to exist in southern Laos, western Vietnam, and eastern Thailand. It became known to zoologists in 1937.

Koupreys are very large ungulates, and can approach similar sizes to the wild Asian water buffalo. These bovids measure 2.1 to 2.3 m (6.9 to 7.5 ft) along the head and body, not counting a 1 m (3.3 ft) tail, and stand 1.7–1.9 m (5.6–6.2 ft) high at the shoulder. Their weight is reportedly from 680 to 910 kg (1,500 to 2,000 lb). Reports of a body mass up to 1,700 kg (3,700 lb) from Vietnam are considered dubious, since they far exceed other recorded weights for the species. Kouprey have tall, but narrow, bodies, long legs and humped backs. They can be either grey, dark brown or black. The horns of the female are lyre-shaped with antelope-like upward spirals. The horns of the male are wide and arch forward and upward, and they begin to fray at the tips at about three years of age. Both sexes have notched nostrils and long tails.