During breeding season, the diets of the Long-legged Buzzards (Buteo rufinus) were studied through pellet and prey remains analysis in arid habitat of northwestern China from 2005 to 2006. By number, mammals 60.00% constituted of the diet, birds 18.00%, reptiles 22.00%. In term of biomass, mammals comprised 87.19% of the diet, birds 6.18%, reptiles 6.63%. The most numerous prey of the Long-legged Buzzards was Rhombomys opimus (48.00%), but Gazella subgutturosa (57.97%) dominated the diet by biomass. Special findings included homing pigeon and a number of nestling and fledging Passerines in the diet. Our results showed that mammals and birds were major prey of breeding Long-legged Buzzard, and results suggest that this Buzzard is an opportunistic hunter and feeds on a wide range of food habitat.