This experiment was conducted to study the effects of sources and levels of dietary selenium on the expression level of mRNA of celluar glutathione peroxidase gene in piglets, and to provide a theoretical basis for the rational application of various selenium sources. Ninety Sanjiang White piglets of 35 days old with similar body weight were selected in the experiment. They were randomly divided into 10 groups with 3 replicates per group and 3 piglets per replicate. Piglets in the 9 experimental groups were fed nano-selenium, yeast selenium and sodium selenite at 0.1, 0.3 and 0.5 mg/kg (by selenium content), respectively. No extra selenium was added to the diet of the control group. The experimental period was 35 days. RT-PCR was used to determine the expression level of mRNA of GPX1 gene in the liver, kidney, spleen, and muscle tissues of the piglets. The results showed as follows: 1) in the liver tissue, the expression level of GPX1 mRNA in nano-selenium group was significantly higher than that in sodium selenite group at 0.5 mg/kg addition level (P<0.05), and the expression level in 0.5 mg/kg nano-selenium group and 0.3 mg/kg yeast selenium group was significantly higher than that in the control group (P<0.05); 2) in the kidney tissue, the differences of the expression level of GPX1 mRNA in all experimental groups were not significant (P>0.05); 3) in the spleen tissue, the expression level of GPX1 mRNA in the nano-selenium group at 0.5 mg/kg was significantly higher than that in the sodium selenite group and the yeast selenium group (P<0.05), and the expression level in 0.5 mg/kg nano-selenium group and 0.3 mg/kg yeast selenium group was significantly higher than that in the control group (P<0.05); 4) in the muscle tissue, the GPX1 mRNA expression level in the nano-selenium group at 0.5 mg/kg was significantly lower than that in the sodium selenite group and the control group (P<0.05). It is concluded that dietary addition of 0.5 mg/kg nano-selenium can increase the expression level of GPX1 mRNA in the liver and spleen tissues of piglets, but in the muscle tissue, the expression level was lower than that in the sodium selenite group and the control group.［Chinese Journal of Animal Nutrition, 2010，22（6）:1630-1635］