Abstract: Seriola aureovittata is a kind of seawater fish with important ecological and economic value. In order to understand the influence of gradual salinity change on osmotic regulation of juvenile Seriola aureovittata, 6 salinity gradient points are set up, which are the natural seawater with salinity of 29 (i.e. the control group) and the seawater with salinity of 5, 10, 15, 20 and 35 respectively, and the gill Na⁺/K⁺ATPase activity, ion concentration and osmotic pressure of the juvenile Seriola aureovittata are detected and analyzed under the conditions of different salinity.In the process of salinity decreasing from 29, the gill Na⁺/K⁺ATPase activity, the ion concentration and the osmotic pressure present a similar law, that is, all showing an overall downward trend with the decreasing of salinity. When salinity goes up from 29 to 35, only the contents of K⁺ in urine and plasma show no significant changes (P>0.05) and all the rest detected indexes are increased significantly (P<0.05). All these results have revealed that the salinity 29 of the natural seawater for Seriola aureovittata to survive and propagate is an optimal salinity for juvenile Seriola aureovittata to survive. In the case of slightly lower salinity 20~29 the juvenile fishes can also adapt quickly. All these indicate that in the process of salinity change the juvenile Seriola aureovittata has strong adjusting ability to the change of external salinity.