Abstract: We studied the change of catalase activity in gill and liver and catalase gene expression in gill of juvenile Amphiprion clarkii at an abrupt change in salinity from 35 to 15 (at decrement of 5, control: 35). The results show that the change of salinity caused no significant difference in survival. The CAT activity in liver and gill of A.clarkii showed an upward trend at salinities of 30, 25, 20 and 15 in 24 h. Besides, thechanging rangeof CAT activity increased with increasing salinity change. All CAT activities had been decreasing since 48th hour and was not different from that of the control till 96th hour (P0.05). The CAT mRNA expressions in gill at salinities of 30, 25, 20 and 15 had been increasing since 6th hour andincreased significantly at 12th hour, which were different from the control significantly (P0.05). All CAT mRNA expression showed no significant difference from the control (P0.05) at 96th hour. Therefore, salinity change had important effect on CAT activity of A.clarkii, and the CAT activities of tissues restored to the normal level in 96 h, showing strong salinity adaptability of A.clarkii.