A 52-year-old man was diagnosed Follicular lymphoma with autoimmune hemolytic anemia. At time of diagnosis his HBs Ag was (+), Anti-HBs (-), and HBV DNA was negative. Chemotherapy was interrupted after tree cycles of R-CVP due to elevated liver enzyme. At that time HBV DNA became positive. Lamivudine therapy was started, whereas patient died due to fulminant hepatic failure. The high morbidity and mortality of this complication is one of the major obstacles to completing the standard treatment for lymphoma in HBV carriers. Thus, preventive therapy with nucleoside or nucleotide analogs should be started before the chemotherapy to prevent HBV reactivation.