Chinese mitten crab, Eriocheir sinensis grows in freshwater habitats until maturity and then migrates into saline waters to spawn.Although it is regarded as an invader causing great ecological and economic loss in European and American countries,the mitten crab has long been a fashionable table delicacy in autumn in China,Japan and other Asian countries.The study was carried out to investigate the changes of external morphological character and some metabolism enzyme activity during the embryonic development of E.sinensis at water temperature(16.2±1.5) ℃ and salinity 20 through laboratory experiment.The results indicated that the process of embryonic development could be divided into nine stages:fertilized eggs,cleavage stage,blastula stage,gastrula stage,eggnauplius stage,eggmetanauplius stage,original zoea stage,prehatching stage and hatching stage.There were significant differences in external morphological character of each stage during the whole process.The whole incubation period is about 40 days at water temperature 16 ℃ and effective accumulative temperature reached 10 758 h·℃.The activity of LDH,total ATPase and MDH changed with the developmental stage of embryos,LDH activity increased first and then dropped with the developmental stage,the highest activity occurred at blastula stage;total ATPase activity was the highest at original zoea stage and was the lowest at gastrula stage; the activity of MDH was the highest at original zoea stage and was the lowest at blastula stage,respectively.