Sepiella maindroni were collected from the wild and the embryonic development of was observed in laboratory. The morphological characters of fertilized eggs and newly hatched larvae between the two species were also compared. The effects of different seawater salinities of 20, 25, 30 (control), 33, 36 for on hatching rate were studied, respectively. Changes in egg fluid osmolality and egg Na⁺/K⁺-ATPase activity of were also measured during the abrupt salinity changes of 192 h, respectively. Hatching rates of fertilized eggs at the same salinity and physiological adaptation to the abrupt salinity changes during 192 h were compared between . The results showed that organ differentiation happened when embryo was 7-day-old, whileS. esculenta. The incubation period of fertilized egg ranged from 21 d to 22 d at 22-24were significantly higher than those under other salinity treatments (<0.01), indicating that salinity of 30 was the fertilized eggs of the two species. Ftilized egg changed as seawater salinity altered during the osmotic pressure of was 60 mOsm/kg higher than those in the medium. fertilized eggs of two species. These results indicate that fertilized eggs of two species have little ability in regulating tilized egg of