The seroprevalence of Brucella infection in yaks was surveyed on the Qinghai-Tibet plateau of China in 2010. A total of 621 serum samples was collected from six counties and were tested by serum agglutination test. The results showed that 56 (9%) of the samples were positive for Brucella. The results of the present investigation indicate that brucellosis is common in yaks on the Qinghai-Tibet plateau of China.