Hepatitis B virus (HBV) reactivation is a well-known complication of lymphoma treatment in the pre-rituximab era. This complication has not been as well studied, however, since monoclonal anti-CD20 antibody became the standard regimen for B cell lymphoma. In this retrospective study, 115 B cell lymphoma patients who received rituximab-containing therapy were analyzed. Of 15 hepatitis B surface antigen (HBsAg)-positive patients, five received lamivudine prophylaxis and did not develop HBV-related hepatitis during lymphoma treatment. Eight of ten HBV carriers without lamivudine prophylaxis experienced HBV-related hepatitis, including one fatal hepatic failure. Four (4.2%) of 95 HBsAg-negative patients developed de novo HBV-related hepatitis and two died of fulminant hepatitis. In conclusion, rituximab-based therapy may cause serious HBV-related complications and even death in both HBsAg-positive and HBsAg-negative patients.