This study was conducted to investigate the effects of dietary supplementation of cottonseed and soybean meal on growth performance of juvenile olive flounder (Paralichthys olivaceus). Nine hundred fish $(0.74{pm}0.11g)$ in the early juvenile stage were randomly divided into 15 groups, and 3 groups were fed one of five isonitrogenous (56% CP) and isocaloric $(16.3;MJ;kg^{-1})$ diets replacing 0, 10, 20, 30, and 40% of fish meal protein by equal proportion (1:1, w:w) of cottonseed and soybean meal (CS) (designated by Control, CS10, CS20, CS30, and CS40, respectively). A solvent extracted cottonseed meal containing high crude protein (44%) and low fiber content (<12%) was used in this study. After 10 weeks of feeding trial, the growth offish fed diets CS10, CS20, and CS30 were not significantly (P>0.05) different compared to that of fish fed the control diet. However, diet CS40 exhibited significantly lower (P<0.05) growth performance than the control diet. No differences were observed in whole body composition of fish fed all the experimental diets. This study indicates that mixture of cottonseed and soybean meal with lysine and methionine supplementation can replace up to 30% fish meal protein in diet for olive founder at the early juvenile stage. However, we suggest that 20% of fish meal protein replacement by cottonseed (10%) and soybean (10%) meal can be the optimum level for commercial use in safety according to the growth performances.