Ulcerative colitis (UC) is one of the most well-known types of inflammatory bowel disease that manifests as recurrent inflammation of rectum and colon. The goal of this study is to evaluate the protective effects of shark liver oil (SLO) on acetic acid-induced ulcerative colitis in rats. Eighty induced UC rats were randomly divided into ten equal groups and received the following treatments for seven days: 1 ml of normal saline rectally, 1 ml of gel base (carboxymethyl cellulose) rectally, 10 mg/kg of Asacol rectally, 10 mg/kg of mesalazine orally, 5% gel form of SLO rectally, 10% gel form of SLO rectally, 200 mg of SLO orally, and 400 mg of SLO orally. We examined the oxidative stress indices, histopathological features, and body weight changes, as well as the function of the liver and kidneys at the end of treatment. Administration of 10% rectal and 400 mg oral SLO resulted in a significant weight gain. Also, glutathione peroxidase activity was significantly higher in 5% and 10% SLO-treated groups, and elevated superoxide dismutase activity in rats that received 5% SLO was observed compared to negative control and Asacol groups. While no significant changes were observed in most of the kidney and liver function markers, higher levels of aspartate aminotransferase were detected in the group that received 400 mg SLO orally compared to negative control and Asacol groups. Many histopathological signs of improvement were observed in mesalazine, Asacol, and SLO groups. There were no significant changes detected in the mean rank among different groups. Our data indicate that SLO supplementation could improve the amelioration of acetic acid-induced UC in rats due to its antioxidant effects.