By means of capillary gas chromatography column , fatty acids composition in diploid and trploid Japanese scallop ( Patinopecten yessoensis) was studied. The main results were as follows : ①The composition of fattyacidsinmuscleandmantlewassimilartobothscallops.Theywereall PUFA >SFA >MUFAandn23PUFA >n26PUFA. The main fatty acids were 22∶6n23(23.9%-28.9%) ,20∶5n23(17.6%-20.6%) ,16∶0(11. 0 % -19.4%) ,18∶0(7.3%-8.1%) and 20∶4n26(2.8%-5.5%); ②Diploid and triploid scallop had similar kinds of fatty acids in gonad ,but there were significant differences in the contents of fatty acids between the two scallops ,in which triploid scallop had significantly higher levels of SFA and MUFA ,but lower level of PUFA in gonad than those of diploid scallop ( P < 0. 01) .