Animal experiments demonstrated that father might transmit HBV vertically via male germ line, however, whether it is really existed in human remains to be determined. Since HBV is a blood-borne virus, the unvaccinated pregnant women would be at risk for HBV exposure if their fetuses carried the virus from fathers. If women had been vaccinated for HBV before conception, what would happen to a maternal immune system if her fetus carried HBV from spermatozoa? However, the literature on transmission of HBV by spermatozoa in vivo is rare, the viral replicating status and fetal immune response in uterus are unknown. The aim of study was to detect father-to-fetus transmission of hepatitis B virus (HBV) in uterus.