We report a case of 48-year old female with rheumatoid arthritis (RA) complicated with myasthenia gravis. In 1988, she was diagnosed of having RA, and several therapeutic drugs were administered, but her disease activity was in poor control. In July 1993, bucillamine (BU) was started at a dose of 100 mg/day, and her arthritis subsided. However, in October 1996, she was admitted with a rapidly progressive ptosis and double vision in the left eye, which became prominent in the evening. Because serum concentration of the antibody to acetylcholine receptors (AchR Ab) was elevated at 12.6 nmol/l, and the ptosis was reversed immediately after a tensilon test, ocular type myasthenia gravis (MG) was diagnosed and it was thought to have been induced by BU. Immunoadsorption therapy was started after discontinuation of this drug, and was continued for 6 months, resulting in improvement of neurological symptoms and decrease in AchR Ab level. MG has not recurred since. Although several cases of D-penicillamine (DP) induced MG are reported, only two cases are reported which were induced by BU, sulfhydryl compound which has a structure similar to DP. Since BU has been widely used as one of the disease modifying anti-rheumatic drugs in Japan, MG induced by this drug should be paid attention as one of the adverse effects.