Blue mackerel scad,Decapterus maruadsi Temminck et Schlegel,is an important pelagic species which is distributed in the coastal areas of China.In the present paper,a total of 444 specimens of blue mackerel scad at fork length(FL)of 52-276 mm were sampled from seasonal lightpurse seine surveys in the East China Sea from May 2008 to February 2009.By analyzing the stomach contents of Decapterus maruadsi,more information was provided on the East China Sea fish feeding ecology.The results showed that more than 80 prey species were ingested by blue mackerel scad,while planktonic crustaceans and smallscale marine fish constituted the dominant prey groups.Among the crustaceans,planktonic larvae,euphausiacea and copepoda made an important contribution to the diet.At the species level,as indicated by the percentage index of relative importance,Benthosema pterotum accounting for 40.44% was the most dominant prey,followed by theSquillidaealima larva accounting for 14.24%,Euphausia pacifica accounting for 11.26%.The percentage of empty stomachs and mean stomach fullness index,which were analyzed by applying the chi-square test and Kruskal-Wallis test,varied significantly among different seasons and size classes.It indicated that the feeding intensity was the highest in spring and lower in winter.Meanwhile,the feeding intensity was the highest in size classes of 50-99 mm and 200-299 mm while the lowest in other size classes.The major diet composition was significantly different among different seasons and size classes.The B.pterotum and Squillidae alima larva were the dominant prey in spring,whereas the planktonic crustacean larvae in summer,B.pterotum and Euphausia pacifica in autumn,Oncaea venusta and mysidacea in winter.Cluster analysis employing Bray-Curtis similarity index revealed there was an abrupt change in diet composition at about 200 mm FL.The planktonic crustaceans were the dominant prey groups of fish smaller than 200 mm FL,whereas smallsize marine fish were the dominant prey for fish greater than 200 mm FL.It indicated that the percentage of nekton significantly increased with the increase of fish size.Compared with the previous studies,the diet composition of D.maruadsi varied significantly,the proportion of B.pterotum decreased markedly.In addition,the average trophic level of D.maruadsi in the East China Sea was 3.55,which was carnivorous fish feeding on plankton and necton.