The present study aimed to investigate the effect of both garlic and yeast (Saccharomyces cervecesa) on survival and growth performance of cultured Nile tilapia (Oreochromus niloticus), besides studying its immune stimulatory and disease control effect via changes in hematocrite value, Nitrobule tetrazolium, neutrophil adherence and lysozome activity, and its impacts on resistance to challenge infection using pathogenic A. hydrophila.