Objective To investigate Hepatitis B Virus (HBV) infection status in placentas of Hepatitis B Surface Antigen (HBsAg) positive pregnant women during middle and late period of pregnancy. Methods One hundred and sixty seven placentas from HBsAg positive pregnant women were collected, including 158 term placentas and 9 aborted second trimester placentas. HBsAg and hepatitis B core antibody (HBcAg) in placental cytotypes were detected by immunohistochemistry. Results Of the 158 term placentas, HBV infection rates in decidual cells (DC), trophoblastic cells (TC), villous mesenchymal cells (VMC) and villous capillary endothelial cells (VCEC) were 66 46% (105/158), 58 23% (92/158), 27 22% (43/158) and 12 66% (20/158), respectively. The HBV infection rates gradually decreased from maternal side to fetal side of placentas. Both HBsAg and HBcAg were mainly located in the cytoplasm of infected cells. The positive cells were mostly in focal distribution. One out of 9 aborted second trimester placentas was infected. Conclusions HBV infection was found in different cells of term placentas. The positive rates for HBsAg and HBcAg in placentas were gradually decreased from maternal side to fetal side. The positive rate was low in aborted second trimester placentas.