Abstract: The effects of salinity on development and Na++2K++2ATPase activity of Marsupenaeus japonicus postlarve were studiedin order to discuss the osmoregulation mechanismof Marsupenaeus japonicus in this paper. It analyzed the feasibility that Marsu penaeus japonicus was cultured in salinealkali area with view of osmotic physiology and provided the scientific basis of culturingMarsupenaeus japonicus using underground brine water.In the test, underground brine water was diluted to the desired salinity levels of 12,16,20 and 24 with yellow river freshwater.Na++/ K++in the water was adjusted to 30 with Potassium chloride (AR).And then Shrimps acclimatized in water of salinity 20 were put into these treatments. Groups of seawater served as the control groups.All trials were conducted in triplicates. In de2velopment test,survival rate and weight gain of Marsupenaeus japonicus postlarve was counted after 72 hours. Count the daily bodyweight gain of the larvae as follows:Daily body weight gain (μg/ indd) =final body weight primal body weightExperiment time number of postlarvesIn Na++2K++2ATPase activity test,the shrimps were sampled at 0h,3h,6h,12h,24h,36h,48h,60h and 72h. The sampleswere preserved in - 20 ℃. The Na++2K++2ATPase was determined by comparison between two media,one of which containing itsspecific inhibitor,ouabain(3mM),without K+according to the method of Esmann. The activity was expressed in micromoles ofinorganic phosphate (Pi) per hr and per mg of protein. Protein was determined according to Bradford’s method with bovin serumalbumin (Sigma) as reference. All the results were given as average of three replicates data and analyzed by ANOVA andDuncan’ s Multiple Range Test.Salinity had significant effectson survival rate,daily bodyweight gain and Na++2K++2ATPase activityof Marsupenaeus japonicus postlarve (p ++2K++2ATPase activities of seawater groups had no significant difference fromgroups of salinity of 30. And along with the salinity change increasing within 48h,the change of Na++2K++2ATPase activities ofpostlarves increased,activites of each treated group presented wave change,and was up to maximum in hyposaline2treated groupsbut up to minimumin hypersaline treated groups till 24h. The Na++2K++2ATPase activityof postlarves tended to be stable from48hto 72h, and was higher while salinity was lower. From above,it suggested that the feasible salinity of Marsupenaeus japonicuspostlarve in hyposaline water was 20 — 24.