Lecithinized-superoxide dismutase (PC-SOD), which is synthesized with a lecithin derivative bound covalently to recombinant human Cu,Zn-SOD, has a longer half-life in blood and higher cell affinity than unmodified SOD. The effects of PC-SOD were evaluated using the rat ulcerative colitis model induced by 3% dextran sulfate sodium. Intravenous injection of rats with 0.5 or 1 mg/kg of PC-SOD suppressed the progression of bloody stools, the formation of erosion, and the infiltration of the colon with inflammatory cells. Furthermore, it also reduced the increase of leukocytes in blood. Thus, PC-SOD may have therapeutic potential in the treatment of ulcerative colitis.