A long‐term feeding trials were conducted to evaluate the effect substituting dietary fishmeal with a mixture of plant and animal protein sources on growth, body composition and economic efficiency of young Korean rockfish (Sebastes schlegeli). A fishmeal‐based diet was designated the control (Con). Three among the other six diets, respectively, had 30%, 40% and 50% of its fishmeal replaced by a mixture of plant and animal protein sources (designated as FS30, FS40 and FS50 respectively), while the remaining three diets were FS30, FS40 and FS50 diets supplemented with L‐lysine and L‐methionine (FS30AA, FS40AA and FS50AA respectively). Three replicated groups of fish (initial body weight, 86 ± 1.9 g) were fed one of the seven diets for 30 weeks. By the end of the feeding trials, the survival rate of all experimental groups was over 92%. The final mean weight, weight gain, feed efficiency, protein efficiency ratio and condition factor of fish were not significantly affected by dietary treatments. Incidence cost of FS50 diet was significantly lower than Con diet. FS50 and FS40AA diets exhibited significantly higher profit index than the Con diet. FS40AA and FS50 diets were the best economically, followed by FS40, FS50AA, FS30, FS30AA and Con diets. These results suggest that the dietary fishmeal could be substituted with a mixture of plant and animal protein up to 50% in the diet without a reduction in growth and feed utilization of young Korean rockfish. Taking account of economic efficiency, the FS50 diet is recommendable for young Korean rockfish farming.