The objective of this study was to determine the effect of supplemented organic selenium at different levels to concentrate feed of Norduz ewes in late pregnancy on maternal serum, placenta, colostrum, and offspring serum concentrations. This study was conducted using two-year-old 35 Norduz ewes. Ewes were randomly assigned to one of three dietary treatments for 57 days prepartum and at the seven days postpartum. Group 1 was fed a standard pregnant sheep concentrate basal diet without any additional Se supplement (control). Experiment groups were fed diets supplemented with 0.150 mg/kg, 0.300 mg/kg, and 0.450 mg/kg organic selenium to the same basal diet. Results showed that addition of selenium to gestating ewe diets increased Se in serum after one week of feeding. Ewes supplemented with 0.300 and 0.450 mg/kg Se had increased placenta, serum, and colostrum Se levels compared with those fed the control diet (P<0.05). There was a strong positive correlation between placental and serum Se concentration in ewes. Colostrum Se increased linearly with dietary Se in the treatment groups. At birth, lamb serum Se ranged from 48.96 ng/mL to 195.52 ng/mL and was affected by the Se concentration of the ewe diets, which indicated placenta transfer of selenium from the dam. As selenium level increased in basal diet, an upward trend was observed in maternal free thyroxine concentration. Likewise, serum free triiodothyronine, free thyroxine, and immunoglobulin G concentrations of lambs from the three treatment groups were significantly greater than of the control lambs. As a result, selenium supplementation was important for maintaining Se and immunoglobulin G concentration in placenta, serum, and colostrum in ewes.