In this study, the purified triacylglycerols (TAG) of selected marine fish oils (anchovy, tuna and salmon oils) were subjected to stereospecific hydrolysis by an sn-1, 3-specific lipase (Lipozyme RM IM) which cleaves selectively the sn-1 and sn-3 position ester bonds of TAG yielding to sn-2-monoglycerides (2-MAG). After lipase hydrolysis, the released free fatty acids and sn-2-MAG were isolated by thin-layer chromatography (TLC). The original TAG and sn-2-MAG were respectively converted to fatty acid methyl esters (FAME), then analyzed by gas chromatography(GC). Results showed that TAG of these marine fish oils were made up of unsaturated fatty acids mainly accounting for 60%. Polyunsaturated fatty acids are preferentially located at sn-2 position, whose percentage is more than 50%, while saturated fatty acids and monounsaturated fatty acids are most distributed in sn-1,3 position. The ratio between n-3 and n-6 PUFAs is greater than 10, which is in line with the FAO/WHO recommended intake standard (> 4) and is ideal for n-3 PUFA natural nutritional supplements.