A 14 weeks growth trial was performed to estimate the protein requirement for growth and maintenance of zebra sea bream (Diplodus cervinus) juveniles. For that purpose, nine isolipidic diets were formulated to contain increasing protein levels (from 50 to 550 g kg−1) at the expense of carbohydrate. Each diet was assigned to duplicate groups of 20 fish, with an average body weight of 7.7 g. Feed efficiency improved with dietary protein up to 400 g kg−1, no further differences being noticed at higher protein levels. Fish fed the 50 g kg−1 protein diet lost weight during the trial. In the other groups, weight gain improved as dietary protein increased up to 350–400 g kg−1. Fish fed diets with 250 g kg−1 protein or lower had lower whole-body protein content than the other groups. A curvilinear-plateau model was used to adjust weight gain and protein gain (g kg ABW−1 day−1) to dietary protein levels. Based on that model, the optimum dietary protein requirement for maximum weight gain was estimated to be 437.6 g kg−1 and for maximum protein gain 461.9 g kg−1, corresponding to a protein intake of 7.63 g kg ABW−1 day−1. Protein requirement for maintenance was estimated to be 1.01 g kg ABW−1 day−1.