A 21-year-old woman with severe aplastic anemia underwent allogeneic bone marrow transplantation from an HLA-identical sibling donor. The patient also had chronic hepatitis B and the donor was an HBV carrier. To decrease HBV and improve hepatic dysfunction before BMT, the patient had received lamivudine for 6 months. After marrow transfusion, administration of lamivudine was continued to inhibit replication of donor-derived HBV. The patient showed hematological engraftment on day 13 without any serious liver dysfunction. Eight months after BMT, she is now alive and well without chronic liver GVHD or reactivation of hepatitis B. HBV-DNA was not detected in the patient's serum. Administration of lamivudine to a BMT recipient with chronic hepatitis B may be a safe and promising way to prevent fatal liver dysfunction in the setting of allogeneic BMT, even in the event of BMT from an HBV-positive donor.