Abstract: Nano red elemental selenium is a kind of nano grain that is dispersed by the protein.The diameter is between 20nm～60nm. The effects of nano red elemental selenium on immune function of mice were resdearched by animal experiment.The rsult revealed that compared with control group,nano red elemental selenium and sodium selenite groups had no significantly changes on the spleen weight,thymus weight,and coefficient of spleen and thymus of mice.The high and middle dose groups of red elemental selenium had signficantly increase on the function of humoral immunity,cellular immunity,and phagocytic function of macrophage of mice,sodium selenite groups had no change on these indexes of mice.Nano red elemental was sensitive in improving the immune function of mice.