Abstract: OBJECTIVE To evaluate the potential role of ω-3 fish oil in the immune function of gastrointestinal cancer patients after surgery. METHODS Computerized searches of the Pubmed, Embase, MEDLINE, Wanfang, CNKI etc. Databases were performed. Randomized controlled trials (RCTs) were included in conformity with the inclusion criteria. The methodological quality assessment was based on modified Jadad rating scale. Research data was extracted by researchers. Revman 5.3 was used to analysis. RESULTS The included trails were 12 RCTs of 848 postoperative gastrointestinal tumor patients. Meta-analysis results showed that the fish oil supplementation resulted increase levels of CD3⁺T cellsWMD=5.79, 95%CI (3.07, 8.50), P<0.01, CD4⁺T cellsWMD=6.22, 95%CI (3.85, 8.59), P<0.01 compared with the isocaloric nutrition regime. And the level of CD8⁺T cells decreased compared with the isocaloric nutrition regimeWMD=-1.74, 95%CI (-2.96, -0.52), P<0.01. CONCLUSION ω-3 fish oil enhances parenteral nutrition effectively enhance immune function of gastrointestinal cancer patients after surgery.