This study was conducted to investigate the effect of in ovo injection of broiler eggs with different levels and forms of selenium on growth performance and some blood parameters of post hatched chicks.  A total of 300 fertilized eggs obtained from a commercial Arbor Acres broiler breeder flock, were used in the present experiment. They were divided randomly into six treatment groups, 50 eggs each. The first one was kept as a control– non injected  group, the second group  (sham)  injected with phosphate buffered saline (PBS), the 3rd and 4th groups were injected with  selenium nanoparticles (SeNPs) at 10 and 20  ug/egg, while the 5th and 6th groups were injected with organic selenium (Se-Methionine) at 50 and 100 ug/egg , respectively.  All eggs were incubated in a forced draught incubator at the recommended temperature, relative humidity and turning patterns .The in ovo injection procedure was done at the 16^th day of incubation. The criteria of response includes: live body weight, weight gain, feed consumption, feed conversion ratio, total protein, albumin, globulin, A/G ratio, cholesterol, triglyceride, HDL and glucose. The results showed that the supplementation of Se did not significantly affect growth performance traits. Supplementation of nano-Se increased plasma concentrations of total protein, albumin and HDL, and decrease glucose, however, no significant differences in globulin, A/G ratio, cholesterol and triglyceride levels. It can be concluded that the use of 20 ug /egg of Nano-Se caused an improvement of growth performance and feed conversion ratio without negative effects on blood constituents.