Portal vein thrombosis is a rare and serious complication in ulcerative colitis (UC). We report a patient with UC who developed portal vein thrombosis with persistent ascites which was successfully managed with total colectomy. A 46-year-old man was admitted complaining of bloody stool. UC had been diagnosed 11 years previously. He required subtotal colectomy because his colitis did not respond to conservative therapy and worsened with suspected peritonitis. Although the portal vein thrombosis was diagnosed after surgery and the systemic anti-coagulant therapy was started, this was stopped after 2 days because of massive rectal bleeding. Fortunately, sufficient hydration with intravenous infusion and re-infusion of concentrated ascites led to portal vein thrombolysis successfully after 28 postoperative days. This case suggests that colectomy and sufficient hydration may have a favorable effect on treatment of portal vein thrombosis in patients with UC.