Human parvovirus 4 (PARV4) has been detected in blood and tissue samples from HIV/AIDS patients who are injecting drug users and we have reported PARV4 co-infection of hepatitis B or hepatitis C virus (HBV, HCV) infected individuals. In this study, we have investigated the consequences of co-infection with PARV4 for HBV infected individuals. The aim of this study was to investigate the consequences of co-infection with PARV4 for HBV infected individuals. Serum samples from healthy controls and HBV infected subjects were retrieved from Shanghai Center for Disease Control and Prevention Sample Bank. HBV genotypes were determined and sequences compared with reference sequences to derive phylogeny trees. All samples were tested for PARV4, parvovirus B19 and HCV; serum alanine transaminase (ALT) in chronic HBV patients was used as an indicator of disease severity.