Nowadays fish culture is one of the best methods by which much protein can be produced. Many countries. now practice fish culture very successfully not only as food industry but as major source of income. Nile tilapia (0. niloticus) was selected as the species for investigation in the present study as it is probably the most extensively cultured tilapia in the world (Bardach et al. 1972). In Egypt, the importance of aquaculture take wide step especially with Nile tilapia that are very palatable for Egyptian people. Therefore, it is essential to develop suitable feed to be used either as a supplementary diet in ponds or as a complete diet in tanks reared with Nile tilapia. For economic and practical reasons these diets must be locally from available protein sources, preferably those unsuitable for direct human consumption. The effect of diets on both specific immune response and nonspecific disease resistance factors have been well studied in homeothermic animals. However, relatively little is known about the relationship between diet and disease resistance in fish. Selected vitamins (particularly C and E) and minerals have been shown to affect immunity and disease resistance in salmonids (Blazer and Wolke, 1984 and Paterson et al., 1985) as well as channel catfish (Durve and Lovell, 1982 and Li and Lovell, 1985). Indeed, quantity and quality of macronutrients, as well as essential vitamins and minerals, are known to affect both the incidence and severity of certain infectious diseases of fish(Wedemeyer and Ross, 1973 and Taniguichi, 1983). In addition, commercial feeds used to maintain laboratory fish for basic immunological, disease susceptibility and toxicological research may be an important source of variation in these studies, even when the fish appear normal and healthy. Therefore, this research was conducted to evaluate the effect of protein sources on the growth performance and disease resistance factors of Nile tilapia (0. niloticus).