-This experiment was conducted in outdoor tanks to evaluate the effect of inclusion of ractopamine at increasing levels (0, 4, 8, 12, and 16 mg kg −1 ) as additive in Nile tilapia (Oreochromis niloticus) diet in the final grow-out period (750-920 g) during 31 days. Therefore, 400 fish were housed into 20 experimental tanks, in a completely randomized design with five treatments and four replications. Growth performance, body yield, and chemical composition of fish muscle and organs were evaluated. Fish fed diets containing up to 16 mg kg −1 of ractopamine for 31 days did not improve growth or performance parameters. However, lipid percentage of abdominal muscle was different in fish fed ractopamine, reaching the lowest level of 199.3 g kg −1 of ether extract at 8 mg kg −1 treatment. Other body chemical composition parameters did not differ between animals treated or not treated. Feeding ractopamine up to 31 days has limited effect on body composition in Nile tilapia (~900 g), without any changes in growth parameters. This is a lower metabolic response in this species when compared with mammals and other terrestrial animals.