It has recently been reported that hepatitis B virus (HBV) reactivation in patients with hepatitis B surface antigen (HBsAg)-negative lymphoma during or after cytotoxic therapy occurs after the use of rituximab and stem cell transplantation for hematologic malignancies. However, clinical data on HBV reactivation in multiple myeloma patients have not been extensively reported. This is the first reported case of HBV reactivation in an HBsAg-negative myeloma patient treated with bortezomib (BOR) as salvage therapy and not stem cell transplantation. By closely monitoring HBV-DNA and early administration of entecavir, severe hepatitis was avoided and BOR therapy was continued. We suggest the importance of close monitoring of HBV-DNA for transplant-ineligible myeloma patients treated with BOR as salvage therapy.