Abstract: Process of changeable characteristic of Procambarus clarkii hemolymph osmotic pressure,gill Na+ -K+ -ATPase activity and three biogenic amines: dopamine,noradrenaline and 5-hytroxytryptamine were investigated in this paper.The results showed that changes of salinity(0‰-20‰) had significant influences on hemolymph osmotic pressure,gill Na+ -K+ -ATPase activity and three biogenic amines(p+ -K+ -ATPase activity declined and came to steady on 6d,having negative correlation with salinity.The gill Na+ -K+ -ATPase have dominant action in the crustacean osmoregulation,which accounting for 70﹪ of the ion transport,and can be taken as an index of osmoregulation.During the experiment,both the biogenic amines contents of hemolymph and gill presented peak values.Dopamine and 5-hytroxytryptamine in hemolymph reached their maximal and minimum values on 1d and 3d,and arrived at stable levels on 6d and 9d respectively.Moreover,Dopamine had negative correlation with salinity,while 5-hytroxytryptamine had positive correlations with salinity.Hemolymph noradrenaline ascended sharply in 0.5d,and took on gental fluctuation during 0.5-3d,then decreased and reached to the control's level.All gill dopamine,noradrenaline and 5-hytroxytryptamine contents gained their maximal values on 2d and all achieved stable levels at the same time,and they had positive correlations with salinity.It is generally believed that the crustacean osmoregulation is controlled by neuroendocrine factors,which were released from incretory organ and distributed rapidly to hemolymph.Many scholars considered that salinity changed in short time,biogenic amines could stimulate phosphorylation of the former enzyme in the gill containing the Na+ -K+ -ATPase,and then ATPase could regulate the ion concentrations in vivo and in vitro.With a long time of adoption,penetrability of gill epithelium to water and ions changed and then the gill Na+ -K+ -ATPase activity came to a steady state.The authors thought that biogenic amines played important role in osmoregulation when salinity altered;biogenic amines induced action of osmoregulation by activating ion transport enzyme Na+ -K+ -ATPase,acclimatizing hemolymph osmotic pressure to environment.