Ulcerative Colitis (UC) is one of the major inflammatory Bowel Syndrome which shows incremental incidence worldwide, with particular occurrence in North America and Middle East. In the present study, the potential protective and curative effects and the molecular mechanisms of Omega-3 polyunsaturated fatty acids (ω-3PUFAs) in rat model of acetic acidinduced UC were investigated. Forty male albino rats were divided into five equal groups. Group I: (Control group) rats received no drugs. Group II: (Early UC-induced group) rats received 2 ml (3% v/v) glacial acetic acid intra-colonially at 21 th day of experiment and sacrificed 3 days later. Group III: (Early UC+ ω-3PUFAs protected group) rats received Omega-3 (300 mg/kg body weight/day) orally for 21 days prior to glacial acetic acid administration and sacrificed 3 days later. Group IV: (Late UC-induced group) rats received glacial acetic acid similar to group II for 3 successive days and sacrificed after 21 days. Group V: (Late UC+ ω-3PUFAs treated group) rats first administered with glacial acetic acid then after 3 days ω-3PUFAs was administered for 21 days. The results showed significant increase in L-malondialdehyde (L-MDA) and myeloperoxidase (MOP) activity with marked decrease in reduced glutathione (GSH) and catalase (CAT) activity in colon tissue of UC-induced rats as compared with control group. However, a significant depletion of colon tissue L-MDA, MOP activity and obvious increase in GSH concentration and CAT activity were observed after ω-3PUFAs administration compared to UC-non treated group. Additionally, a significant upregulation of mRNA gene expression levels of interleukin-1β (IL-1β), Caspase-3 and downregulation in B cell lymphoma-2 (Bcl-2) were observed in colon tissue of UC-induced rats. However, the expression levels of IL-1β and Caspase-3 were down-regulated, and Bcl-2 was up-regulated after administration of ω-3PUFAs. These results suggest that, ω-3PUFAs protect rats' colonic mucosa against acetic acid-induced UC as evidenced by histopathological studies and may be effective in enhances the healing of UC via anti-inflammatory and anti-apoptotic activities and regenerating endogenous antioxidant mechanism.