We report a case of rheumatoid arthritis (RA) complicated by myelodysplastic syndrome (MDS) successfully treated by tacrolimus. A 57-year-old woman had persistent pain and swelling in bilateral wrist and knee joints, in addition to severe anemia and leukopenia. She was diagnosed with MDS and RA based on the results of bone marrow aspiration and the criteria of RA. Combination therapy with tacrolimus (1.5 mg day(-1)) and prednisolone (10 mg day(-1)) improved her bicytopenia and polyarthralgia.