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, the changing range of CAT activity increased with increasing salinity change. All CAT activities had been decreasing since 48^th hour and was not different from that of the control till 96^th hour (P>0.05). The CAT mRNA expressions in gill at salinities of 30, 25, 20 and 15 had been increasing since 6^th hour and increased significantly at 12^th hour, which were different from the control significantly (P < 0.05). All CAT mRNA expression showed no significant difference from the control (P>0.05) at 96^th 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.