Hepatitis B virus (HBV) reactivation in patients previously positive for hepatitis B surface antibody (HBsAb), so-called reverse seroconversion, has been considered to be a rare complication after hematopoietic stem cell transplantation (HSCT). We experienced two patients who developed reverse seroconversion among nine who were HBsAb positive and Hepatitis B core antibody (HBcAb) positive before HSCT; one after autologous bone marrow transplantation (BMT) and another after allogeneic peripheral blood stem cell transplantation (PBSCT). We reviewed the literature and considered that reverse seroconversion of HBV after HSCT is not uncommon among HBsAb positive recipients. The use of corticosteroids, the lack of HBsAb in donor, and a decrease in serum HBsAb and HBcAb levels may predict reverse seroconversion after HSCT.