The aim of this study was to explore the effects of parenteral supplementation with ω-3 fish oil emulsion (Omegaven ) on systemic inflammatory response syndrome (SIRS) during the ini-tial stage of severe acute pancreatitis (SAP).In a prospective,randomized and controlled trial,60 pa-tients with SAP were randomized either to treat with conventional therapy (Con group,n=30) or conventional therapy plus intravenous supplementation with 0-3 fish oil emulsion 0.2 g/kg every day (FO group,n=30).The effects were analyzed by the SIRS-related indexes.The results showed that APACHE-II scores in FO group were significantly lower,and the gap increased much farther after the 4th day than those in Con group (P<0.05).Fluid equilibrium time became shorter markedly in FO group than in Con group (5.1±9.2 days vs 8.4±2.3 days).In FO group,SIRS scores were markedly duced,while IL-10 decreased markedly,most prominently between the 4th and 7th day,and the ratio euteral supplementation with ω-3 fish oil emulsion could efficiently lower the magnitude and persis-tence time of the SIRS,markedly retrieve the unbalance of the pro-/anti-inflammatory cytokines,im-prove severe condition of illness and may provide a new way to regulate the SIRS.