Abstract: The characteristic indexes for constituents of thirty-four fatty acids in fifty-five kinds of fish oil were analyzed by gas chromatography.The results comparing the constituents of other animal oil and plant oil showed that fish oil had highy contents of unsaturated fatty acids,among which the amounts of essential fatty acids such as EPA and DHA were relatively higher, the characteristic indexes were 5.2%-20.0% and 5.7%-25.9% respectively.They were the most important fatty acids constituents in fish oil and were the index to evaluate the quality of fish oil.The amounts of C18:2n6 and C18:3n3 were lower (0.6%-2.7% and 0.2%-2.5%,respectively).The balance of essential fatty acids in feedstuff was important.Different kinds of fish oils had different characteristic indexes of fatty acids, the indexes were distinctly different from other animals and plants oil, it was the basis to distinguish the kinds of fish oil, to discern the false fish oil from the genuine.