The aim of the present study was to compare the effects of oral administration of nanoparticles-selenium and selenit sodium on peripheral blood factors in sheep. For the purpose fifteen sheep, were randomly divided to three groups and to groups 1 nanoparticles-selenium (1mg/kg), prepared by selenium dioxide reduction using ascorbic acid, to groups 2 selenit sodium (1mg/kg) and to group 3 as control group distilled water were orally given for 10 consecutive days. Then, the blood sample were collected from the jugular vein of all sheep into the tubes containing heparin on days 0, 10, 20 and 30 and on them were determined the hematological factors including hematocrit, erythrocytes, hemoglobin, white blood cell, platelet and total protein concentration was determined by autoanalyzer. For differential cell counting, after the preparation of candle flame smear, were fixed by methanol and were stained with giemsa for 20 minutes. Then the cells number of neutrophils, eosinophils, basophils, monocytes and lymphocytes differential count were by lens 100 of optical microscopy and cedar oil. Statistical analysis in the hematocrit, erythrocytes, hemoglobin, platelets, fibrinogen and total protein showed no significant difference among the three groups on different days. But the survey of the white blood cells count showed a significant increase in group1 on day30 with day 0 and means comparison in group-1 with control group on day 30. Also, the neutrophils count determined a significant increase ingroup 1 on day 30 with day 10 and means comparison in group-1 with two and control groups on day10. The survey of the lymphocytes count showed a significant decrease inmeans comparison in group-1 with two and control groups on day10. The study revealed nanoparticles-selenium compared with sodium selenite increase, the number of white blood cells and neutrophils with greater intensity.