Hepatitis B virus (HBV), distributed throughout the world, is classified into seven geographically separatedgenotypes designated A to G. Since the prevalence of HBV infection in isolated ethnic Tibetan populations in China,and the HBV genotypes involved have been hither to remained unclear, we collected 262 blood samples from fourisolated villages in the east and west regions of Tibet. The prevalence of HBV infection was estimated by EIA forHBV Ag and HBV Ab. The HBV genotypes were determined by a PCR-microwell plate hybridization method usingplasma DNA. The prevalence of HBV Ag and HBV Ab positives was 19.1% (50/262 cases) and 29.0% (76/262 cases),respectively. We detected only the C genotype (20/20 cases), this being known as a predominant type of HBV amongMongoloid populations in Asia. The results revealed, for the first time, that Tibetan villagers have a high rate ofinfection with HBV of C genotype, in line with the available data for chronic hepatitis and liver cancer.