Inroduction & Objective: The supplementation of selenium in animal nutrition is useful after a decline in performance due to selenium deficiency of diet. As nutritional technologies progress, new Selenium supplements such as nano selenium are available, which requires research and comparison with previous products. Thus, the aim of this study was the evaluation of selenium sources effect on performance, blood metabolites and immune response in Holstein and Holstein-Mont Bilyard Hybrid calves. Material and Method: 24 sucking Holstein and Holstein-Mont Bilyard calves with mean body weight of 43± 1 kg were divided in a completely randomized design for 75 days. The experimental treatments included: 1-basal diet without supplementation of selenium for Holstein-Mont Bilyard calves, 2-basal diet without supplementation of selenium for Holstein calves, 3-basal diet+0. 3 mg/kgDM supplementation of nano-selenium for Holstein-Mont Bilyard calves, 4-basal diet+0. 3 mg supplementation of nano-selenium for Holstein calves, 5-Basal diet + 0. 3 mg/kgDM Sodium selenite for Holstein-Mont Bilyard calves, 6-basal diet + 0. 3 mg/kgDM sodium selenite for Holstein calves. The daily feed intake of calves and body weight gain and the concentrations of metabolites such as glucose, urea, triglyceride, cholesterol, total protein, glutathione peroxidase enzyme activity and the percent of lymphocyte, neutrophil and monocyte of blood samples were determined. Results: There was no significant effect on performance and also on blood glucose, cholesterol, triglycerides, urea and immune response in calves. But blood total protein and glutathione peroxidase activity increased in calves. In general, the source of supplements was not effective in the level of glutathione peroxidase activity of treatments. Conclusion: There was no significant effect on performance and blood parameters of Holstein and Holstein-Mont Bilyard calves.