Abstract: We studied the changes in serum cortisol and Na⁺ -K⁺-ATPase activities in gill and liver of juvenile Amphiprion clarkii at an abrupt change in salinity from 35 (control) to 15 at decrement of 5. The results show that salinity changes had no significant effects on survival but affected serum cortisol and Na⁺ -K⁺-ATPase activities of the juveniles significantly (P < 0.05). The concentration of serum cortisol showed a downward trend after the juveniles were abruptly transferred to low salinities in 24 h, then all decreased to the control level at 48^th hour and even lower than control level at 96^th hour, showing no significant difference. The trends of Na⁺ -K⁺ -ATPase activity in gill and in liver were highly consistent. The Na⁺ -K⁺ -ATPase activities in the two tissues increased obviously in 24 h, then sharply declined in the same way as serum cortisol level at 48^th hour and 96^th hour (P>0.05). In summary, the variation amplitude of these physiological indices mentioned above showed a positive correlation to the salinity decreased degree. Therefore, there is a significant impact of salinity changes on the concentration of serum cortisol and Na⁺ -K⁺ -ATPase activity of A.clarkii. It is revealed that A.clarkii has strong salinity adaptability.