Abstract: The study was designed to investigate the embryonic development of N eomysis japonica with the histologicalechnique,meanwhile,analyze the relationship among the length of the female adult,the number and the length of theewly hatched larvae stastically. The study indicated that the whole process of the embryonic development of N eomysis ja-onica occurred in the marsup ium,lasting 8 days (176-188h) on average. The whole process of the embryonic develop-ent was divided into 3 main phases by the shedding of the membrane and the ecdysis,the main phaseswere divided into substages. The 3 phaseswere egg stage,eyeless stage and eye stage,respectively. Egg stage was subdivided into zygoteubstage,blastula substage,gastrulae substage and egg-naup lius substage; eyeless stage was divided into naup lius sub-tage and egg-metanaup lius substage; eyestalk substage was the other name for eye stage. The duration of the egg stage ac-ounted for -1. -% (40h) of the whole developmental time on average; the eyeless stage was the main stage of the whole rocess of the embryo development,which took about 48. 9% (9-h) of the whole developmental time on average,gut androtch of antenna,heart and p igment of eyespot and segment of abdomen were observed during this stage; eye stage lasted7. 6% (5-h) of the whole development period. Both the number and the length of the newly hatched larvae were demon-trated to be highly dependent upon the length of female adult. This study may provide more information related to basiciology of mysid and guidance for the artificial breeding of mysid.