Objective  To investigate the effect of omega-3 fish oil emulsion on the inflammatory responses, immune function, and prognosis of patients after liver transplantation. Methods  Thirty-six patients undergoing orthotopic liver transplantation at the Liver Transplantion Center of No. 81 Hospital of PLA from January 2009 to December 2010 were enrolled in this study. The patients were randomly divided into two study groups: the fish-oil group, in which patients were given omega-3 fish oil emulsion (n=18), and the control group (n=18). All the patients received isocaloric and isonitrogenous nutrition for six days, starting on the day after the operation. Blood samples were obtained pre-operatively and on the 2nd, 5th, and 8th days post-operation to measure cytokines (IL-1β, IL-2, IL-6, IL-10, TNF-α), C-reactive protein (CRP), and lymphocyte subpopulation (CD4, CD8, HLA-DR). The incidence of infection, and acute rejection, mortality, length of ICU stay, and postoperative length of hospital stay were also recorded. Results  The cytokine levels after liver transplantation in all the patients were higher than those before operation. The IL-1β, IL-2, IL-6, and TNF-αlevels in the fish-oil group were significantly lower than those in the control group (P<0.05 or P<0.01). CRP level in the fish-oil group was significantly lower than that in the control group on the 5th postoperative day (POD5) (P<0.01). The CD4/CD8 ratio in the fish-oil group was significantly higher than that in the control group on POD5 (P<0.01). In addition, the IL-10 and TNF-αlevels in the fish-oil group were significantly higher than those in the control group (P<0.01). HLA-DR⁺ lymphocyte count in the fish-oil group was significantly lower than that in the control group on POD8 (P<0.05). The incidence rate of infection in the fish-oil group (16.7%) was significantly lower than that in the control group (55.6%, P=0.035). Moreover, the incidence rate of acute rejection and mortality showed no statistical difference between the two groups. However, patients in the fish-oil group had significantly shorter postoperative ICU and hospital stays (3.9±1.9d, 28.6±7.2d, respectively) than the control group (5.8±3.1d and 35.7±10.6d; P=0.034, P=0.024, respectively). Conclusion  The administration of omega-3 fish oil emulsion to liver transplant patients can reduce excessive inflammatory responses, maintain the balance of pro-/antiinflammatory cytokines, modulate the immune function, lower the incidence of infection, and improve prognosis.