Mice were injected intraperitoneally with hydrocortisone acetate to replicate the animal model of Kidney Yang Deficiency (KYD). Osthol and total-coumarins (TCR) from the fruit of Cnidium monnieri were administered orally to model mice. The effects of osthol and TCR on the immunological function of the KYD mice were observed. The results showed that compare with those in normal mice, the percentage of phagocytosis and the index of macrophage phagocytosis, the level of serum hemolysin and the proliferation of lymphocytes lowered significantly (P < 0.01) in model mice. It was shown that administering osthol or TCR could notably (P < 0.01) prevent the above-mentioned lowering in model mice, revealing that osthol and TCR could improve the immunological function of KYD mice.