This report describes a 58-year-old man with rheumatoid arthritis (RA) and interstitial pneumonia who suffered from low-grade fever, abdominal pain, and bloody diarrhea 16 months after the diagnosis of RA. Ulcerative colitis (UC) was diagnosed, based on endoscopic and histological findings. RA associated with UC is rare and the underlying mechanism is unknown. We discuss here whether vasculitis and HLA class may play some role in the association of RA with UC.