A total number of 210 unsexed (Arbor Acres) broiler chicks at 7 day of age were used to investigate the effects of different sources of Selenium i.e. inorganic (Sodium selenite (SS), organic (Saccharomyces cerevisiae with Se and Zn / Se-Methionine/Se-Glycine/ Se-Yeast and Saccharomyces cerevisiae with Se) on the productive performance, blood hematological and biochemical constituents and immune response of broiler chicks. Experimental chicks were randomly divided into seven dietary treatments with six replicate cages per treatment, five chicks each. The first group was fed the basal diet without supplementation (control); while the 2^nd, 3^rd, 4^th, 5^th, 6^th and 7^th groups were fed basal diet supplemented with 100 ppm/kg diet of the above mentioned Se sources, respectively. Results showed that chicks fed the basal diet supplemented with different sources of Se had significantly better BW, BWG and FCR compared with control group. Organic Se supplementation improved growth performance of broilers compared with the inorganic one. Supplementation of different Se sources decreased serum levels of cholesterol and LDL, whereas RBCs count, hemoglobin, PCV, glucose, globulin, thyroid hormones, immune response (IgA- IgM, IgG), and antioxidant enzymes activity were significantly increased compared with the control. In conclusion, Se supplementation improved the growth performance, immune response and physiological status of broiler chickens. Broilers fed organic Se-supplemented diets had better growth performance and immune response than those fed inorganic selenium