Effects of different salinity (12, 16, 20, 24, 28, 32, and 36) on serum ions and digestive enzyme activities were investigated in this study. Results showed that salinity caused significant influences on serum ions and digestive enzyme activity in Parapenaeopsis hardwickii(P<0.05). The concentrations of serum K⁺, Na⁺, Cl^- dramaticlly increased with salinity rising , and the isoionic points were estimated as 10.01, 159.87, and 195.10 mmol/L, of which the corresponding salinity is 36.5, 18.3, and 13.7, respectively. Highest activity of pepsin occurred at salinity of 12, then it reduced with salinity rising. Highest activities of trypsin and lipase occurred at salinity of 24.The peak of amylase activity occurred at sanilities of 12 and 24. From a zymologic standpoint, optimal salinity range for Parapenaeopsis hardwickii was 24 to 28.