The therapeutic effect of olsalazine on ulcerative colitis mice was evaluated by measuring disease activity index (DAI), colonic mucosal injury index (CMDI), histopathological score (HS), and detected the expression levels of interleukin (IL)-2, IL-10, tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), IL-1β in serum and IL-7, IL-17, IL-22, epidermal growth factor (EGF), transforming growth factor β1 (TGF-β1) in colonic homogenate of mice. The gene discussed is IL17A; the disease is ulcerative colitis.