Detailed observations of the embryonic developmental stages of E. possjeticus were obtained by using vivo light microscopy. The embryonic development and its relationship with incubation temperature were studied. The results indicated that there was a positive linear relation between the fecundity and female body length. E. possjeticus displays a direct development, with the eggs developing inside a ventral brood pouch, where they hatch as larvae. The duration of embryonic development was about 220 hours at the constant temperature 21℃. There were two types of observations for embryonic development. One was isolated culture and the other was the fertilized egg carried by the female. The result showed that the fertilized egg of the isolated culture and the fertilized egg carried by the female developed almost simultaneously in the same conditions. In a word, eggs undergo total cleavage for the first few times, and then turn to the superficial cleavage. Early total cleavage appears to be a general feature of amphipod embryogenesis. The hatched larvae had similar morphological characters to those of adults. Temperature showed significant influence on the embryonic development time. Within range of water temperature 15-27℃, the duration of embryonic development decreased with the increase of temperature, while the developmental rate increased. Based on the developmental time at the different temperature, the developmental threshold temperature was calculated to be 6.02℃, and sum of effective temperature was 137.30℃·d.