Abstract: To screen the optimal fermentation time of Zhiqi fungal substance, effects of zhiqi fungal substance from different fermentation days on specific and nonspecific immune function of immunodeficiency mice were investigated by experiments of mouse carbon clearance, phagocytosis of chicken red blood cells, determination of hemolysin, Ig M and Ig G in mice serum, mouse spleen lymphocyte proliferation.The results indicated that zhiqi fungal substances after 25 and 30 days' fermentation had both distinct immune-enhancing-effect ( p < 0.05, 0.01; 0.05) , which hinted they could obviously strengthen immunocompromised population's immunity.