Summary 　Dietary supplementation of ω3 polyunsaturated fatty acid（PUFAs）including eicosapentaenoic acid（EPA）and docosahexaenoic acid（DHA）has been held to be beneficial for human diseases in which inflammation is suspected as a key component in pathogenesis. Also, elevation in ω3 PUFA levels in ω3 desaturase（fat-1）transgenic mice that endogenously biosynthesizeω3 PUFA fromω6 PUFA led to effective protection against inflammation and tissue injury. Several possible mechanisms to explainω3 PUFA’s actions are proposed：preventing conversion of ω6 arachidonic acid to pro-inflammatory eicosanoids, serving as an alternative substrate producing less potent products, or being converted to potent anti-inflammatory mediators（i.e. resolvins and protectins）. These metabolites may underlie some of the beneficial actions of ω3 PUFAs in controlling inflammation and related diseases.