To investigate the interaction between HBeAg and CD81.The CD81 gene was amplified by RT-PCR from HepG2 cells. The recombinant expression vector pGADT7-CD81 was constructed by routine molecular biological method. The auxotroph yeast cells were cotransfected with pGADT7-CD81 and pGBKT7-eAg and plated on synthetic dropout nutrient medium (SD/-Trp-Leu-His-Ade) containing x-alpha-gal. The binding of HBeAg to CD81 was also detected in vitro translation and coimmunoprecipitation test.The recombinant expression vector was constructed and confirmed by restriction enzyme (EcoR I and BamH I) digestion and DNA sequencing analysis. The positive yeast clones could grow and from blue colonies on SD/-Trp-Leu-His-Ade/x-alpha-gal medium. The result of immunocoprecipitation showed that HBeAg could bind to CD81.HBeAg can bind to CD81, suggesting that CD81 plays an important role in the pathogenesis of HBV.