Hepatitis B virus (HBV) reactivation has previously occurred in hepatitis B surface antigen-negative patients with malignant lymphoma who received rituximab-based combination chemotherapy. However, few reports have described cases of HBV reactivation in patients with multiple myeloma thus far. We report a case of HBV reactivation in a patient with multiple myeloma treated with chemotherapy, autologous hematopoietic stem cell transplantation, and maintenance steroid therapy. For the HBV reactivation, the patient was treated with the antiviral agent entecavir. The clinical symptoms and laboratory findings improved after 3 months. Further studies should target the identification of patients at high risk of HBV reactivation in multiple myeloma treated with autologous hematopoietic stem cell transplantation and steroid therapy for maintenance and establish viral prophylaxis strategies, especially in Korea, in which HBV infection is endemic.