Fish culture is an important element of many rural development programs in areas suffering from animal protein shortages. Tilapias are one of the most popular fish for culture and have been introduced into many countries around the world. In recent years, attention has been focused on developing tilapia culture. We studied the effects of a dietary supplementation of beta-glucans on Nile tilapia (Oreochromis niloticus). Two-hundred-seventy fingerlings (mean mass ± SD =40.7 ± 0.4 g) were separated into six groups of 270 fish; G1 (control normal) was fed a basal diet, whereas G2 (control infected). G3 (betaglucan 0.5% normal), G4 (betaglucan 1%normal), G5 (betaglucan 0.5% infected), G6 (betaglucan 1% infected). Each group was fed for 12 weeks to evaluate growth performance, and to evaluate immune status and disease resistance and some biochemical and histopathological parameters. The best growth and feed utilization were observed in G4. Serum IgM values were significantly higher in G4 than G1.Fish that were fed the betaglucan had better relative percent survivability after challenge with Aeromonas hydrophilla. We could recommend that dietary supplementation with β-G improves the performance of Nile tilapia and possesses an immunostimulating effects. Keywords: β-glucan; Nile Tilapia; Aeromonas hydrophilla; Immunostimulant effects.