The objectives of this work were to study the effects of salinity change on the physiological chemical factors of Epinephelus coioides juvenile (body weight: 19.59 ?0.25g) by a biochemical analysis. The gill Na /K -ATPase, plasma glucose, aspartate carbamyl transferase (AST) , the activity of SOD and lysozyme of Epinephelus coioides juvenile were assayed after treated with salinity [(4，14，24 and 34 as contro1)] in 1, 3, 6 and 9 d At the same time, the gill chloride cells were observed using an H-E staining. The results showed that Na /K -ATPase activity in all groups showed similar tendency and the concentration reached the maximum level on 3rd day, then decreased and keep it constant on 6th day. The number of gill chloride cells did not show significant difference in salinity 24, but decreased slightly in salinity 14 during the experiment period. The changes in number, nucleus size and color of gill chloride cells in salinity 4 were observed on 6th day. The serum glucose level in all groups showed similar tendency and the concentration reached the maximum level on 6th day, after then decreased. The serum AST level showed similar tendency both in salinity 24 and in salinity 4 and the concentration reached the maximum level on 9th day. However, the serum AST level continuously decreased in salinity 14 during the experiment period. The hepatic SOD activity in all test groups showed a tendency of decreasing at the beginning and increase later, and reached the minimum level on 3rd day. There were significant differences in the hepatic SOD activity among all test groups (P <0.05). The serum lysozyme activity in all test groups showed a tendency of increasing at the beginning and reached the maximum level on 6th day, then decreased and gradually stable. There were significant differences in serum lysozyme activity among all test groups (P <0.05). When the salinity gradually decreased from 34 to 24, 14 and 4, these physiological chemical indicators showed similar tendency in all test groups, suggesting that E. coioides is typical of broad salinity fish and possesses good adaptability to low salinity. The results showed that E. coioides juveniles could adapt to the water body of salinity 4 under salinity domestication.