Abstract: This study was conducted to evaluate the efficiency of different selenium (Se) sources and levels in corn-soybean meal broiler diets. For that, 400 day-old unsexed Arbor Acres broiler chicks were allocated to 10 experimental treatments in a 5 (sources) x 2 (levels) factorial arrangement. Five Se sources were tested; (1) sodium selenite (NaSe) as inorganic form; (2) selenomethionine (Se-Yeast) as organic form; (3) Zinc-L-selenomethionine (Zn-Se-Meth) as more recent organic form; (4) powder form of Nano Se form (P-Nano Se) and (5) Liquid form of Nano Se (L-Nano Se). Also two inclusion of Se levels in diets; 0.15 and 0.30 ppm, were examined. The inorganic and organic forms of examined Se were obtained from commercial suppliers while both powder and liquid forms of Nano Se were prepared immediately before starting feeding phases of the experiment. The prepared 80 nm Se nano-particles were synthesized by chemical reduction method and characterized by Transmission Electron Microscope, X-ray diffraction and spectrophotometry. Three phases (1-10, 11-24 and 25-40 d) of feeding were applied and all birds were kept under similar management conditions. Parameters of growth performance, carcass characteristics and concentration of Se in both liver and thigh muscles were investigated. Also assay of Malnodialdhyde (MDA) was carried out in frozen (6 months at -20°C) thigh muscles to investigate the oxidation status of broiler meat. The obtained results showed significant improvement of growth performance and Se concentration in liver and thigh tissues either due to using organic or nano forms of Se, or by increasing the inclusion Se level from 0.15 to 0.30 ppm in broiler diets. While carcass abdominal fat%, giblets% and MDA content in thigh muscles did not affected due to Se sources or levels. Liver showed grater Se concentration than thigh muscles. The overall experimental results showed that using Se-Yeast or Zn-Se-Meth as organic forms of Se, or L-Nano Se as nano form of Se at level of 0.30 ppm in broiler diets or its equivalent in drinking water, respectively, is more effective to get better growth performance and quality of broiler meat. But further studies about the safety of using nano form of selenium as feed additives are needed.