This study was carried out to evaluate the effects of in ovo injection of copper nanoparticles on the performance and immune system of broilers. Fertile eggs from Ross 308 breeder broiler flock were divided into 4 groups as follows. The group was injected with one mL of physiologic serum and the groups injected with copper nanoparticle solutions at doses of 50, 75 and 100 ppm in the air cell, at the first day of incubation. The daily feed intake and average daily gain at the rearing period was higher in 100 ppm group (P <0.05), while there was no diference in feed conversion ratio. There was no diference in antibody titers against the influenza virus. The higher and lower antibody titer against Newcastle virus were observed in the group injected with 75 ppm and 100 ppm nano-Cu injected group, respectively (P <0.05). Total white blood cells and heterophils in broilers at 10 days of age were decreased in 50 ppm nano copper group (p <0.05), however, the lymphocytes of the same group (50 ppm) was significantly increased (P <0.05). The hematocrit percentage of blood samples at 10 days of age in broiler chickens in 100 ppm nao copper group decreased (P <0/05). A linear decrease in serum triglyceride levels was observed with the in ovo injection of 75 and 50 ppm copper nanoparticles compared to the control group (P <0.05). Serum cholesterol and HDL levels in the 50 ppm copper nanoparticles groups  were lower than the group of 75 ppm copper nanoparticles and the control group (P <0.05). Serum LDL levels were not affected by experimental treatments. The results of this study showed the positive effect of in ovo injection of copper nanoparticles, especially at 50 ppm level on feed intake, growth rate, and feed conversion ratio and serum cholesterol and triglyceride levels.