To explore the effect of natto powder on the immunological function in mice.MethodsNatto powder were consecutively orally administered to mice with different dosage for 30 d. Humoral immunity, cellular immunity, phagocytic system function and activity of natural killer cell were used to access the effect of natto powder on immunological function. ResultsNatto powder could stimulate proliferation and transformation of mice's spleen lymphocytes, promote delayed hypersensitivity, increase the quantity of antibody producing cells, enhance the level of serum hemolysin, accelerate the carbon clearance and intensify the peritoneal macrophage, and had no significant effect on activity of natural killer cell in mice.ConclusionIt suggested that natto powder could enhance the immune function in mice.