This study evaluated fermented soybean meal (FSM) as a fish meal (FM) replacement and determined the appropriate amount of FSM in juvenile olive flounder diet. Twenty-four aquaria with a flowing-water system were stocked with fish averaging 20.9 g at a density of 25 fish/tank. Five experimental diets were prepared replacing FM with 0, 10, 20, 30, or 40% FSM based on FM protein (designated $FSM_{0}$, $FSM_{10}$, $FSM_{20}$ $FSM_{30}$, and $FSM_{40}$, respectively). Two additional diets were prepared that replaced 30 or 40% of the FM with FSM with added amino acids (methionine and lysine) (designated $FSM_{30+AA}$, and $FSM_{40+AA}$, respectively). Fish (triplicates) were fed one of the eight experimental diets (50% crude protein and 16.7 kJ available energy $g^{-1}$ diet) for 8 weeks. Survival did not differ among the treatments during the feeding experiment. There were no significant differences in weight gain (WG) or specific growth rate (SGR) among the fish fed diets with up to 30% of the FM replaced. However, fish fed $FSM_{40}$ or $FSM_{40+AA}$ had a reduced WG and SGR, as compared to $FSM_0$ (control) (P < 0.05). The feed efficiency and apparent digestibility showed a similar trend (P < 0.05). The proximate composition in the whole body of fish differed only between the control and $FSM_{40}$ for the crude protein level and between the control and $FSM_{30+AA}$ for the crude lipid level. The whole-body amino acid composition did not differ among treatments. No significant differences were found between the diet groups with and without amino acid supplementation, indicating that amino acid supplementation had no effect. The major finding of this study is that fermented soybean meal may replace up to 30% of fish meal without amino acid supplementation for normal growth of juvenile olive flounder.