The effects of selenium supplements were investigated on blood glutathione peroxidase activity (GPX), selenium, copper, zinc, iron and weight gain. Twelve female Makuei breed, aged nearly 2 months old and weighed approximately 20 kg was studied for 63 days in 3 groups of control, nano selenium particles (NanoSe) and sodium selenite (NaSe). Mean concentrations of GPX, Cu and Fe were high in NanoSe but the differences were not significant. Among sampling time, it was significant constantly for GPX and Se, occasionally for Cu and Zn but not for weight gain. The percentages of weight gain based on birth weight in groups control, Nano SE were 34. 2%, 38. 9% and 36. 3%, respectively, all were not different among groups and sampling times. The individual comparison of parameters in 40 lambs among groups showed differences for GPX, Se and Cu (P<0. 01). Correlations were found between weight/Fe, weight/GPX weight/Se, Zn/Fe and GPX/Se in NanoSe. In conclusion, Se supplements increases GPX activity and Se in which the increases in NanoSe was regular and continues. Se supplements showed no negative effects on Cu, Zn and Fe but caused partially increase in weight gain. NanoSe revealed the correlations between weight gain, GPX, Fe and Se and was priority to NaSe. Thus, the effects of NanoSe in reduce the oxidative stress and increased weight gain was appropriate and probably reasonable option to NaSe administration in lambs.