A 65-year-old woman with a 25-year history of rheumatoid arthritis (RA) was admitted because of acute pneumonia in January, 1991. Then she was pointed out M proteinemia (IgG 3,220 mg/dl, IgA 139 mg/dl, IgM 216 mg/dl) for the first time. Serum IL-6 was below 4.0 pg/ml. She was followed up because of lack of bone change. Plasma cell count in bone marrow were 14.6%. She was re-admitted because of development of bone lesions March, 1992. There was no joint pains, and serum IgG, IgA and IgM were 5,148 mg/dl, 114 mg/dl and 106 mg/dl, respectively. CRP was negative. Serological tests of rheumatoid factor and antinuclear antibody were both positive. Serum IL-6 was elevated to 14.8 pg/ml. Bone marrow aspiration disclosed 30.6% myeloma cells. Serum IgG, A, and M were 5,148 mg/dl, 114 mg/dl and 106 mg/dl, respectively. Serum immunoelectrophoresis showed monoclonal IgG with kappa type light chain. X-ray findings revealed radiolucent myelomatous foci. From these findings, IgG kappa-type multiple myeloma with RA was diagnosed.