Background/aims: Reactive oxygen. species have a known potent role in the pathogenesis of ulcerative colitis. Roprost, a pharmaceutical, is a chemically stable derivative of a naturally- occurring human prostacyclin. Several studies have demonstrated protective effects of iloprost via its antioxidant and its anti-inflammatory activity. The aim of this study is to evaluate the effects of iloprost on oxidant/antioxidant status, as well as the large bowel histopathology in experimental colitis. Materials and Method: Forty adult male Wistar-albino rats were randomly divided in to four equal weight-matched groups: sham group (n=10), iloprost administered sham group (n=10), colitis group (n=10), iloprost administered colitis group (n=10). Acetic acid (1 ml of 4% solution) was used to induce colonic inflammation in the rats. Results: Colonic tissue and plasma malondialdehyde levels were significantly lower in the iloprost administered colitis group than the colitis group (p<0.01). Tissue glutathione levels of the iloprost administered colitis group were significantly higher than the colitis group (p<0.001). Conclusion: We have demonstrated in this study iloprost to be an antioxidant, as well as iloprost demonstrating protective activity against colitis induced oxidative stress.