[ Objective] The aim was to study the protein polymorphism in the blood of Tibetan Mastiff, and provide some theoretical basis for resource protection and reasonable development and utilization of Tibetan Mastiff varieties. [ Method] A total of 103 blood samples were taken from four populations of Hequ Tibetan Mastiff, Qinhai Tibetan Mastiff, Tibetan Spaniel and native dogs of Qinghai. Seven blood protein Iocus(Tf, Po, Sα2, Hb, AIb, Pr and Amy)were investigated by using vertical polyacrylamide gel electrophoresis with discontinuous buffer system. Then the genetic variation during different populations was analyzed. [ Result] Genetic variations were observed in Tf, Sα2 and Po in four populations, others were not polymorphic. There were three alleles at the locus of Tf and Po, two alleles at the loci of Sα2. Effective number of alleles and Nei's average expected heterozygosity were 1. 532 4 and 0.230 3 relatively, all higher in Tibetan Mastiff than other populations. [ Conclusion] Protein locus in blood of Tibetan Mastiff existed in genetic variation.