We examined the processes associated with Osmoregulation in Caspian kutum following their sudden entrance into the waters with 6 and 11 ppt salinity. We sampled the whole body and gill tissues of Caspian kutums for parameter measurements on 24, 72 and 168 hours after exposure to different salinities. The enzyme Na⁺/K⁺ ATPase in the first group (6 ppt) at 24 hrs after exposure, increased significantly compare to control group (P<0.05) and decreased but did not show any significant difference (P>0.05). In 11 ppt salinity, the maximum enzyme concentration was seen in 24 hour after exposure again, and then decreased, but it was higher compare to control group (P<0.05). Protein content in 6ppt salinity did not differ significantly compare to control but in other group, the protein decrease with significant difference. The Osmolarity of the second group increased with a greater slope than the first group, but at all time, they differed significantly (P<0.05). The RNA concentration in 6 ppt, had not any significant difference compared to control (P>0.05), but in 11 ppt, decreased with significant difference (P<0.05). The mortality rate was 7.33±1.52 % in second group and we did not see any mortality in 6 ppt concentration as well as controls. The water content decreased with the salinity enhancement (P<0.05). The results of this study illustrates that, all the indicators fluctuations reached desirable point after 7 days, so releasing them into the environments near to Caspian Sea with more salinity because of escaping from several pollutants in estuaries would be better.