Juvenile giant grouper were fed six experimental diets, one control diet for 8-wk to investigate the dietary optimal requirement for protein. The test diets were supplemented with fish meal and casein in various ratios (35, 40, 45, 50, 55, 60％). The results show lowest growth were observed when the grouper were fed on the diet having the lower crude protein (35 and 40％). The diet with ca. 50％ crude protein ensures adequacy of the grouper for protein.