Summary Background Inulin and oligofructose promote selective growth of saccharolytic bacteria with low inflammatory potential. Objective To test the effect of oligofructose‐enriched inulin in patients with active ulcerative colitis. Design Prospective, randomized, placebo controlled pilot trial. Eligible patients had been previously in remission with mesalazine as maintenance therapy or no drug, and presented with a relapse of mild to moderate activity. They were treated with mesalazine (3 g/day) and randomly allocated to receive either oligofructose‐enriched inulin (12 g/day, p.o., n = 10) or placebo (12 g/day of maltodextrin, p.o., n = 9) for 2 week. Primary endpoint was the anti‐inflammatory effect as determined by reduction of calprotectin and human DNA in faeces. Results Rachmilewitz score decreased in both groups, reaching statistical significance at day 14 (P < 0.05). Oligofructose‐enriched inulin was well‐tolerated and dyspeptic symptoms scale decreased significantly with active treatment but not with placebo. At day 7, an early significant reduction of calprotectin was observed in the group receiving oligofructose‐enriched inulin (day 0: 4377 ± 659 µg/g; day 7: 1033 ± 393 µg/g, P < 0.05) but not in the placebo group (day 0: 5834 ± 1563 µg/g; day 7: 4084 ± 1395 µg/g, n.s.). Changes in faecal concentration of human DNA were not significant. Conclusion In active ulcerative colitis, dietary supplementation with oligofructose‐enriched inulin is well tolerated and is associated with early reduction in faecal calprotectin.