BACKGROUND AND AIMS: Curcumin has anti-inflammatory properties. The aim of this study was to evaluate the effect of curcumin on improvement of the disease activity in ulcerative colitis (UC). METHODS: In this randomized double-blind clinical trial, 70 patients with mild-to-moderate UC were randomly assigned to curcumin (1,500 mg/day) or placebo intake for 8 weeks. Disease clinical activity, quality of life, serum levels of tumor necrosis factor alpha (TNF-alpha), high-sensitivity C-reactive protein (hs-CRP), erythrocyte sedimentation rate (ESR) values, and complete blood count were measured. RESULTS: Changes in Simple Clinical Colitis Activity Index score were significantly higher in the curcumin than the placebo group (-5.9 +/- 2.08 vs. -2.1 +/- 2.6; p = .001). The scores of Inflammatory Bowel Disease Questionnaire-9 and quality of life were significantly higher in the intervention group compared to the control group (p = .006). Furthermore, the curcumin supplementation reduced the serum hs-CRP concentration (-6.3 +/- 13.6 vs. 3.7 +/- 11.6 mug/ml; p = .01) and ESR levels significantly (-1.6 +/- 2.7 vs. -0.09 +/- 2.4 mm/hr; p = .02) in comparison with the control group. No significant changes were observed in the TNF-alpha levels of both groups. CONCLUSIONS: Consumption of the curcumin supplement, along with drug therapy, is associated with significant improvement of the clinical outcomes, quality of life, hs-CRP, and ESR in patients with mild-to-moderate UC.