BACKGROUND The herbal extracts Curcumin and QingDai were previously shown to be effective in mild-moderate and in moderate-severe ulcerative colitis (UC), respectively. We evaluated the efficacy and safety of a combination of curcumin-QingDai (CurQD) in patients with active UC. METHODS This was a two parts trial. Part 1 was an open label study of 4 weeks CurQD in patients with active UC, defined by a Simple Clinical Colitis Activity Index (SCCAI) score ≥5 and a modified Mayo endoscopic sub-score≥2. Part 2 was a placebo-controlled trial conducted in two centers in Israel and Greece, that randomized active UC patients at a 2:1 ratio to either enteric-coated CurQD 3gr/day or an identical placebo for eight weeks. The co-primary outcome at week 8 was clinical response (reduction in SCCAI of ≥3 points) and an objective evidence of response (Mayo endoscopic subscore improvement of ≥1 or 50% calprotectin reduction from baseline). Responding patients continued either Curcumin or placebo alone for additional 8 weeks as maintenance treatment. Expression of Cyp1A1 in rectal mucosa was assessed as a measure of aryl-hydrocarbon receptor (AhR) pathway activation. Curcumin purity, and indigo and indirubin content in CurQD were confirmed by LC-MS/MS. RESULTS 59 patients were enrolled in the two study parts. In efficacy analysis of part 1, 7/10 responded including 3/10 who achieved clinical remission. For part 2, 95 patients were screened and 42 were included and randomized. The co-primary outcome was achieved in 43% and 8% of CurQD and placebo patients, respectively (p=0.033). Clinical response was observed in 85.7% versus 30.7% (p CONCLUSION In this randomized controlled trial, combination CurQD was found to be effective for inducing remission in active UC patients. Induction of AhR may merit further study as a potential treatment target in active UC.