Background and aims: Ulcerative colitis (UC) is a prevalent and long-term condition that causes inflammation, irritation, and ulcers in the colon. This systematic review aimed to evaluate the effect of seafood oil omega-3 supplementation on UC remission. Methods: PubMed, EMBASE, Web of Science, and Scopus databases were extensively searched on 25.5.2022 according to the PRISMA checklist. The studies were imported into EndNote X9. Data were extracted in Excel form, including the first author’s name, study setting, year of publication, sample size, sea oil type, intervention, and outcomes. Results: Seafood oil omega-3 supplementation reduced the levels of leukotriene B4, interleukin (IL)-2, IL-8, IL-1β, thromboxane A2, prostaglandin E2, scavenges-free radicals, and tumor necrosis factor-α (TNF-α). In addition, supplementation with this oil could decrease free radicals at the cellular level and subsequently increase antioxidant activity, which also mediates the inflammatory process itself. Conclusion: Most studies showed that omega-3 extracted from seafood can reduce inflammation and oxidative stress (OS) in intestinal cells. It also could improve clinical symptoms and scores of histological, sigmoidoscopic, and simple clinical colitis activity index (SCCAI). However, some studies reported no positive effects in this regard and confirmed that these compounds have no effect on improving UC symptoms.