Osthol and total coumarins of Fructus Cnidii were given to the model of Kidney-Yang Deficiency rats induced by hydrocortison acetate injection, the changes of serum concentration of thyroxine T3, reverse T3 (rT3), T4 and thyroid stimulating hormone (TSH) were observed. Results showed that in comparison with normal rats, all of the criteria mentioned above were lowered significantly (P < 0.01) in model rats. After treatment, the criteria observed were all increased significantly (P < 0.01 or P < 0.05). It was suggested that the osthol and total coumarins of Fructus Cnidii could elevate the pituitary-thyroid axis function of Kidney-Yang Deficiency rats.