An 8-week feeding trial was conducted to evaluate the effect of fish meal replacement by soybean meal on growth and intestine morphology in red pacu (Piaractus brachypomus). Five isonitrogenous and isocaloric diets formulated containing 32.04 ± 0.46 crude protein and 17.26 ± 0.31 KJ gross energy g^-1 diet. The control diet was formulated to contain 50% fish meal, whereas in the other four diets soybean meal was included at 16.5, 33, 49.5 and 66% to replace 25 (SMP25), 50 (SMP50), 75 (SMP75) and 100% (SMP100) of the fish meal protein. One hundred and ninety fish (with average weight 1.8 ± 0.07g) were randomly distributed into five treatments (each treatment included 3 replicates). After 8 weeks of feeding, weight gain and specific growth rate in SMP25 and SMP50 diets were significantly higher than other treatments (P<0.05). Feed consumed in fish fed SMP50 diet were significantly higher than other treatments (P<0.05). Feed convention ratio in SMP100 diet was significantly higher than fish fed other treatments. No differences in inflammation and atrophy were observed among different treatments but villous length were significantly higher in SMP25 and SMP50 treatments (P<0.05). The results of the present study indicated that soybean meal can be replaced up to 50% of fish meal protein in red pacu diet and this may allow production an economical diet without negative effect in growth performance.