This study was aimed to evaluate the effect of a probiotic and a prebiotic on growth performance and intestinal morphometry of Nile tilapia (Oreochromis niloticus). The experiment had lasted 70 days and it was used 144 fingerlings with initial average weight of 1.1 ± 0.2g and 4.0 ± 0.2cm total length of Chitralada lineage, acquired from a commercial fishfarm. The fish were housed in nine boxes of fiber-cement with a util volume of 200L, distributed in a completely randomized design and feed with a commercial ration, only or supplemented with probiotics (Bacillus subtilis) or prebiotics (mannan-oligosaccharides). It were used the following treatments: commercial diet only, commercial diet + probiotic; commercial diet + prebiotic. There was no difference between the values of final biomass, average weight gain, average daily weight gain, gain in total length, survival index, apparent feed conversion ratio and hepatosomatic index. There was no difference between treatments for intestinal villi number, but the fish that received treatments with the addition of probiotics or prebiotics showed greater villus height and those that received the treatment with the probiotic had even a greater thickness of the villus epithelium, compared with animals feed with ration without additives.