Korea is an endemic area for hepatitis B virus (HBV) infection. Reactivation of HBV is a well-recognized complication in patients with chronic HBV infection undergoing cytotoxic or immunosuppressive therapy, and there are some reports of hepatitis B reverse seroconversion after HSCT. This study evaluated changes in HBV serology after HSCT. We reviewed the medical records of 141 patients who had available HBV serologic data after autologous HSCT. Patient information was retrospectively collected from the BMT database. Before transplantation, 12 patients were positive for hepatitis B surface antigen (HBsAg) and received lamivudine prophylaxis. There was 1 case of reactivation of HBV among these patients. One hundred twenty-nine patients were negative for HBsAg before HSCT, of whom 110 were positive and 19 were negative for hepatitis B surface antibody (anti-HBs). Sixty-two of the 110 patients who were positive for anti-HBs were also positive for hepatitis B core antibody (anti-HBc). Eight patients were negative for anti-HBs and anti-HBc. Seven patients who were initially negative for HBsAg were identified as positive after HSCT, and 5 of those 7 patients developed acute hepatitis, thus indicating reverse seroconversion. Univariate analysis showed that reverse seroconversions were observed more frequently with multiple myeloma than another disease (P = .005; relative risk, 11.854; 95% confidence interval, 1.381-101.770). Other factors, such as age, sex, and presence of HBcAb before HSCT, had no statistically significant affect on reverse seroconversion. In conclusion, reverse seroconversion of HBV is not a rare complication of autologous HSCT, and the risk of reverse seroconversion after treatment is a serious concern due to possible complications arising from patients' suppressed immune systems.