Heat stress is one of the major problems of tropical and subtropical areas of the world, adversely affecting the production performance of poultry. Heat stress suppresses broilers immunity against disease, body weight gain and increases mortality rate in the flock. The avian gastrointestinal tract is populated by a diverse and dynamic microbiota, generally considered important for host nutrition and immunity. About 300 to 500 bacterial species reside broilers gut. The key functions of the gut microbiota in host health and well-being includes nutrients digestion and absorption,and significant up-regulation of innate and acquired immunity.There are quite a few studies depicting effect of heat stress on gut microbiota. Perturbations in the GIT micobial composition that occur as a result of stress can be settled by prebiotics or probiotics supplementations. These two supplements are also known for promoting growth performance and immunity of broilers. However, use of these supplements in broilers reared under tropical environment has not been examined. Therefore, we planned this project to examine effects of heat stress and pre/probiotics on broilers health and performance.