Classical polyarteritis nodosa (PAN) is a term that includes patients with necrotizing inflammation of medium-sized arteries and excludes those with microscopic vessel involvement. Although gastrointestinal manifestations are not unusual in patients with classical PAN, the association with ulcerative colitis has been reported only rarely. We describe a patient with classical PAN complicated by bilateral renal artery aneurysms with subsequent rapture and perirenal hemorrhages. He was successfully treated, and the bilateral renal aneurysms resolved with steroid therapy. Two years later, the patient presented with hematochezia. Colonoscopy revealed inflamed rectal mucosa with bleeding ulcers. Histologic findings of biopsy specimens showed severe mucosal inflammation and crypt abscess. The patient was diagnosed with ulcerative colitis, and the symptoms attenuated after meselazine therapy.