The serum contents of IL-23 and IL-17 in the patients with ulcerative colitis and the clin. significance were studied. Forty patients with ulcerative colitis as UC group and 30 healthy people as control group were selected. The serum contents of IL-23 and IL-17 were determined by ELISA. Serum contents of IL-23 and IL-17 in UC group were higher than those in control group significantly (t=18.76, 21.48, P<0.01). Serum contents of IL-23 and IL-17 increased with the clin. symptoms. Serum contents of IL-23 and IL-17 in severe patients were higher than those of mild and moderate patients significantly, and serum contents of IL-23 and IL-17 in mild patients were higher than those of moderate patients significantly. Serum contents of IL-23 were pos. correlated to IL-17 significantly (r=0.548, P<0.01). IL-23 and IL-17 participates in the pathogenesis of ulcerative colitis. IL-23 may play a critical role in the development of UC through inducing production of IL-17.