【Objective】This experiment was conducted to study the effects of different Se sources on production performance，thyroid level and immune function in sows during lactation.【Method】A total of 200 LY（Landrace×Yorkshire）binary hybrid multiparous sows（healthy，with similar body condition，close due date，3-6 parities）were allotted to 10 groups randomly，with 20 replications in each group. Group one was the control group fed with basal diet without supplementation of Se. The other 9 groups were supplemented with 0.3，0.5 or 0.7 mg·kg^-1 Se-containing sodium selenite，yeast selenium or nano-selenium respectively. The whole feeding experiment lasted for 58 days.【Result and conclusion】The birth mass of group supplemented with yeast selenium by 0.3，0.5 mg·kg^-1 or nano-selenium by 0.5，0.7 mg·kg^-1 was significantly higher than that of the control group（P＜0.05）.The group with 0.5 mg·kg^-1 selenium yeast was significantly higher than those of the control group and the group with sodium selenite in mass of weaning litter，litter mass gain and daily gain（P＜0.05）.The effect of different sources of selenium on 3，3′，5-triiodothyronine（T₃）and 3，5，3′，5′-thyroxine（T₄）mass concentrations in serum of lactation sows and sucking piglets was extremely significant （P<0.01）.Compared with the control group，groups with sodium selenite or selenium yeast，the serum T₃ mass concentration of sows fed on the diets supplemented with nano-selenium group significantly（P<0.01）increased by 29.52%，17.24% or 23.63%，respectively，but the serum T₄ mass concentration significantly（P<0.01）decreased by 24.71%，30.88% or 33.86% respectively. Compared with the group with sodium selenite or selenium yeast，the serum IgA and IgM mass concentration of sows fed on the diets with nano-selenium increased by 85.39% and 79.35%（P<0.01）or 24.19% and 50.98%（P<0.01）respectively. Compared with the control group，the serum IgG mass concentration of sucking piglets from the sows fed on the diets with sodium selenite， nano-selenium or selenium yeast significantly（P<0.01）increased by 19.11%，43.39% or 34.63% respectively，while the serum IgA and IgM mass concentration increased by 93.67%，160.75% or 132.91% and 90.91%，140.91%or 102.27% respectively.The results indicate that nano-selenium or selenium yeast supplemented in diets can significantly improve the reproductive performance and immune function of sows，and regulating the secretion of thyroxine.