Abstract: We investigated the survival, growth and changes of gills of juvenile milkfish (Chanos chanos) under freshwater acclimation. At the end of the 30-day experiment, the survival rate, weight gain rate and specific growth rate were recorded; the gills of juveniles were observed and compared with those cultured under freshwater without acclimation and sea water. The highest survival rate (100%), weight gain rate and specific growth rate of juveniles were obtained under freshwater acclimation. Large numbers of mitochondrion-rich cells were observed on branchial lamellae of juveniles in freshwater. It might be one of reasons for the high survival rate of juvenile C.chaos under condition of freshwater.