An experiment was designed to investigate the effects of dietary selenium on performance, carcass traits, blood biochemicals, tissues selenium deposition, antioxidant activity and immunoglobulin of broiler chicks. Total of 210 day old broilrer chicks were divided into seven dietary treatment groups with three replicates each. Control group (T₁) was fed with basal diet contain the recommended level of selenium of Arbor-Acres broiler chicks cataloge, as a source of inorganic selenium. Experimental groups; T₂, T₃ and T₄ were given basal diet free of selenium, but supplemented with 0.1, 0.2 and 0.3 g selenium yeast/ kg diet, T₅, T₆ and T₇ were fed basal diet free of Se and supplemented with 0.01, 0.02 and 0.03 g nano-selenium/ kg diet, respectively. Results showed that chicks fed diet supplemented with 0.03g nano-selenium/ kg diet (T₇) had significantly (P ≤ 0.05) the highest values of daily weight and improved feed conversion ratio compared to the other treatments which also recorded the least feed intake. Se-yeast or nano-selenium showed higher some carcass traits, liver meat of breast and thigh Se contents and high density lipoprotein, while low density lipoprotein, concentrations were significantly (P ≤ 0.05) decreased. Activity of glutathione peroxidase, in serum blood was significantly (P ≤ 0.05) increased by supplementation of 0.03 g nano-selenium/ kg diet compared to the control group and other treatments. Also, chicks fed diet supplemented with 0.03 g nano-selenium/ kg diet had the highest livability rate (98%) and the best European efficiency rate (443.5%) but it was less economically efficient and relatively economic efficiency may have been due to the high price of nano-selenium at the present time compared to organic selenium. So, the obtained results in the present study encouraging and indicated that 0.3 g selenium yeast/ kg diet (T₄) can be used in broiler chicken diets to get best economic efficiency and higher relative economic efficiency. It could be concluded that addition of organic and nano-selenium in broiler diets positively affects production performance and various parameters of broilers health.