We encountered a rare case of aortic regurgitation due to rheumatoid arthritis. A 53-year-old man was admitted with severe heart failure due to aortic regurgitation. He had been treated for rheumatoid arthritis for 5 years with methotrexate. After treatment for heart failure, his aortic valve was successfully replaced with an Omnicarbon prosthetic valve. Histopathological examination of the excised aortic valve showed rheumatoid granuloma. His post-operative course was uneventful.