Abstract: Background and Objective: The prevalence of Ulcerative Colitis (UC) in most countries has increased and it is necessary to develop new therapeutic options for UC. Siegesbeckia pubescens is a traditional Chinese medicine widely used for the treatment of inflammatory and autoimmune diseases in clinic. The purpose of this study is to evaluate its therapeutic effect against UC. Materials and Methods: Experimental UC in rats was induced by iodoacetamide (IA) through instilling into the lumen of the colon. The aqueous extract of S. pubescens (SPA) was orally administered 3 days before IA instillation and continued upto 4 days. Throughout the experiment, rats were monitored for body weight loss, stool consistency and fecal occult blood which were quantified as Disease Activity Index (DAI). At the end of the experiment, rats were sacrificed and colonic length, weight, macroscopic and histopathological damage were examined. Furthermore, the mRNA expression levels of pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β) were analyzed in the colonic tissues by real-time PCR. The data were examined for their statistical significance of difference with ANOVA and the standard’s t-test. Results: The results showed that SPA significantly ameliorated typical symptoms of IA-induced rat colitis including weight loss, mucus stool and bloody diarrhea. Moreover, macroscopic and histopathologic scoring showed that SPA suppressed IA-induced colonic edema, hyperemia, necrotic destruction of epithelium and inflammatory cellular infiltration. In addition, SPA inhibited IA-induced pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β) mRNA expression in colon. Conclusion: These evidences indicated that SPA has therapeutic effects against IA-induced colitis in rats which suggested the potential of S. pubescens as an agent for use in the treatment of UC for the first time.