The activity of Na⁺/K⁺ ATPase in branchial epithelium, concentration of ions (Na⁺, K⁺, Cl^-) and osmolarity in serum of Acipenser schrenckii, during salinity acclimation, were measured and analyzed in this paper, and the osmotic re gulation process was discussed. The activity of Na+/K+ATPase in different salinities (10,20,25) was significantly higher than that in control group, which increased by 2 or 2.5 times. Na⁺/K⁺ATPase activities under different salinities decreased in the beginning, and increased with the acclimated time elapsing, finally decreased again and tended to be stable. Osmolarity in serum was elevated with the rising salinities. The highest value was (328.77±26.78) mmol·kg^-1 in salinity 10. Hereafter, the osmolarity decreased gradually and kept in about 290 mmol·kg^-1. The value was a little higher than that in control group. In all acclimated salinities, the changes on activities of Na⁺/K⁺ ATPase and serum osmolarity showed the same trend. The concentration of K⁺ in 3 different salinities was rising, but the difference was not significant(P>0.05) than that in control. The average of K⁺ concentration kept between 3.0 and 3.20 mmol·L^-1. The trend of Na⁺ and Cl^- concentration changes in serum was similar. The concentrations of Na⁺ and Cl^- were elevated under salinity 10, but the difference was not significant (P>0.05) than control. The concentration of Na⁺, Cl^- in serum under 20 and 25 salinities were not significantly different. The osmotic regulation might be divided into 3 phases by analyzing the data in this paper. One is the stress. The obvious symptom is the decrease of Na⁺/K⁺ATPase activities. The second phase is active regulation, which is characterized by that the Na⁺/K⁺ ATPase is activated and its activity is elevated. The last phase is the adaptation. In this phase, the Na⁺/K⁺ ATPase activities decrease again and are inclined to be stable.