To study the effects of nano elemental selenium (Nano-Se) or sodium selenite (Na2SeO3) on the activities of glutathione peroxidase (GSH-Px) and Type-I deiodinase in the liver. A total of 234 weanling pigs (Duroc x Landrace x Yorkshire) at an average initial body weight of 8.3 kg were allocated to 13 treatments. The thirteen dietary treatments were basal diet only (containing 0.04 mg/kg Se), basal diet + 0.1, 0.2, 0.3, 0.4, 0.5, 1.0 mg/kg Se as Na2SeO3 or Nano-Se, respectively. The results were as follows: Supplementation with 1.0 mg/ kg Se as Na2SeO3 reduced (P < 0.05) growth performance and GSH-Px activities as compared with the addition of a concentration range of 0.20-0.40 mg/kg Se. When Nano-Se was added to the diet, the growth and GSH-Px activities remained steady at the peak value as at a concentration of 1.0 mg/kg Se; There were no difference in the activities of GSH-Px between the treatments of Nano-Se and Na2SeO3 when added concentration of Se was 0.10-0.40 mg/kg. The pigs had higher (P < 0.05) activities of GSH-Px at a concentration range of 0.50 and 1.0 mg/kg as Nano-Se than Na2SeO3; Supplentation with Se increased the activity of Type- I deiodinase in liver, however, the increased extent was affected by neither Se sources nor added concentration of Se. The results implicated that for the best concentration range of Weinberg curve, Nano-Se is wider than Na2SeO3.