Sixty non-pregnant Rahmani x Romanov crossbred ewes used to study the effect of selenium on production and reproduction performance of ewes. The experimental ewes divided into five similar groups based on age, body weight, and physiological state (12 head/group), the first group (G1) used as control group without any addition. The second and third groups were injected with 0.1 mg (G2) or 0.2 mg/kg DM (G3) of selenium (sodium selenite), or oral of 0.1(G4) or 0.2 mg/kg DM (G5) of nano selenium. Fertility (%) of pregnant ewes were 83.3, 91.7, 100, 91.7 and100% in G1, G2, G3, G4 and G5, respectively. Total protein (g/dl) blood were 7.1, 6.06, 6.4, 5.9 and 6.1 for G1, G2, G3, G4 and G5, respectively and corresponding values of globulin (g/dl) were 2.22, 2.54, 2.40, 2.05 and 2.38. The values of GOT were 79.2, 60.25, 69.07, 79.2 and 60.25 (U/L) and the values of GPT were 28.71, 15.61, 12.2, 16.5 and 20.6 (U/L). Thyroid hormones as T3 and T4 were 3.2, 4.2, 4.1, 4.36 and 4.65 (ng/ml) for T3 and 6.7, 6.6, 7.09, 6.84 and 7.33 (ng/ml) for T4 on G1, G2, G3, G4 and G5. The present study showed that giving Se to pregnant ewes improved the immunity of their lambs during the suckling period.. Finally, it can conclude that used of 0.1 or 0.2 mg/kg oral Nano-selenium could favorable effects on lambs performance.