PURPOSE: To investigate the effect of medical ozone treatment on the experimental acute distal colitis in rats. METHODS: Eighteen rats were randomly distributed into three equal groups; control, acute distal colitis (ADC) without and with medical ozone treatment. Rats in the control group were taken saline. ADC was performed by rectal way with 4% acetic acid in groups 2 and 3, and the group 3 was treated with medical ozone for three weeks both rectally and intraperitoneally. At the twenty second day the distal colons samples were obtained for malondialdehyde and myeloperoxidase, blood samples were obtained to measure the levels of TNF-α and IL-1β levels. Histolopatological examination was evaluated with Ki-67, IL-1β and VEGF immunostaining densities. RESULTS: There was significant increase in tissue MDA, MPO activity, TNF-α and IL-1β after ozone administration. There was also a significant difference at immunostaining densities of histopathological examination. CONCLUSIONS: Medical ozone treatment ameliorated the experimental acute distal colitis induced by acetic acid in rats. Its possible effect is by means of decreasing inflammation, edema, and affecting the proliferation and the vascularization.