This feeding trial was conducted to evaluate the effects of replacing soybean meal with fermented brewer's grain levels on the growth performance, body composition and serum biochemical indices of juvenile hybrid tilapias (s). Five hundred and forty juveniles with an initial weight of (3.00±0.08) g were randomly divided into six groups, with three replicates of 30 fish. Six isonitrogenous and isoenergic experimental diets were formulated to contain different levels of fermented brewers' grains to replace soybean meal at 0, 20%, 40%, 60%, 80% and 100%, respectively. The experiment was performed for 60 days in anindoor recirculating culture system. The results showed that there were no significant differences in weight gain, specific growth ratio, feed efficiency and protein efficiency ratio when the replacement level was 0-60% (>0.05). When the replacement level was more than 60%, the growth performance of the fish was significantly lower compared with the control group (<0.05). Based on weight gain and feed efficiency by quadratic regression analysis, the best replacement ratios of soybean meal with fermented brewer's grain were 54.1% and 55.4%, respectively. The crude lipid contents in the whole body and muscle decreased as the replacement level increased, while the moisture and ash contents showed the opposite trend (>0.05). Meanwhile, the viscerosomatic index (VSI) and hepatosomatic index decreased with increasing dietary fermented brewer's grain level (>0.05). When the replacement level was 100%, the VSI was significantly lower than in the control group (<0.05). The activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and the glucose content significantly increased as the replacement level increased; when the replacement level was more than 40%, serum ALT and AST activities were significantly higher than in the control group (<0.05). When the replacement level was more than 20%, the glucose content was significantly higher than in the control group (<0.05). In addition, the triglyceride and cholesterol contents were reduced with increasing dietary replacement level; when the replacement level was more than 60%, serum cholesterol levels were significantly lower than in the control group (<0.05). Meanwhile, when the replacement level was more than 40%, serum triglyceride levels were significantly lower than in the control group (<0.05). Based on the results of growth performance, body composition and serum biochemical indices, the optimal replacement level was 54.1%-55.4% for juvenile hybrid tilapias.