A patient with Non-Hodgkin's lymphoma is reported, in which reactivation of the hepatitis B virus was achieved from treatment with rituximab. The patient's HBs antigens were positive on admission, and she tested positive for HBs, HBe, and HBc antibodies, and negative for the HBe antigens. She was treated with a regimen of three courses of rituximab-containing anti-cancer drugs and one course of combined anti-cancer drugs. Throughout these chemotherapy courses, prednisolone was not given. After the fourth course of chemotherapy with the third rituximab she developed hepatic dysfunction, and the serum titers of HBs and HBc antibodies suddenly decreased. After administration of lamivudine, however, she gradually recovered from liver failure.