The present study was carried out to explore the protective effects of probiotic and N-acetylcysteine (NAC) on acetic acid induced ulcerative colitis. Thirty two adult albino rats were divided into four equal groups; control group, ulcerative colitis group, Probiotic group and NAC group administered (1.62 g/kg) probiotic and (108 mg/kg) NAC respectively for 18 days. After one week of the experiment the ulcerative colitis, Probiotic and NAC groups received intracolonic injection of 2 mL acetic acid 4% for four days for induction of ulcerative colitis. Probiotic and NAC administration significantly decreased the activity of colonic myeloperoxidase (MPO), and down-regulated the inflammatory markers gene expression which were up-regulated by acetic acid. In addition, colonic catalase (CAT) and superoxide dismutase (SOD) activities and glutathione (GSH) concentration were increased by probiotic and markedly increased by NAC comparing to ulcerative colitis group while malondialdehyde (MDA) concentration decreased. Moreover, Probiotic and NAC exhibited protective action against the immunohistochemical and histopathological changes induced by acetic acid in rat colon. In a conclusion, probiotic and NAC had significant ameliorating effects against acetic acid induced ulcerative colitis possibly attributed to their anti-inflammatory and antioxidant properties.