Abstract: The study investigated the variations of hemolymph osmolality and gill Na+/K+-ATPase activity in juvenile ark shell (Anadara broughtonii) (shell length 25~35 mm) under different salinity stresses. The results show that the hemolymph osmolality under abrupt stress at salinities of 20, 25, 35 and 40 decreased significantly or fluctuated ascendingly then became stable in 48 h. At salinity of 15, the juveniles needed 96 h to complete the adjustment. At a changing salinity rate of 5d-1, the hemolymph osmolality at salinity of 40 tended to be stable in 48 h but in 72 h at salinity of 15, which was faster the previous change than at salinity of 15. After an abrupt decrease in salinity, the Na+/K+-ATPase activity of gills increased significantly in 12 h and each treatment reached its peak in 24 h. Then the activity quickly dropped and returned to a steady state higher than the control, and with an abrupt increase of salinity, it fluctuated descendingly and reached the bottom in 12~24 h lower than the control. The activity changed much less at salinity of 15 and 40 than at sudden-change salinity. In conclusion, the response patterns of Na+/K+-ATPase activity of gills under different salinity stresses were different, i.e., the activity increased under low salinity stress but decreased under high salinity stress. It is suggested that gradual salinity change would be helpful for A.broughtonii to adapt to salinity stress.