Bao-Chun-Wan, a Chinese prescription, is formulated according to the principle of tonifying the kidney for treatment of aging. Morphological study on the ultrastructure of laboratory albino rats treated with this formula showed an increase in thymic lymphocytes, which play an important role in the production of T cells. As to the liver cells, the formula has a protective effect and may induce enzymes enhancing oxidation and excretion of toxic substances. An increase in the Leydig's cell, which promotes reproductive hormone secretion, was also observed, but there was no obvious change in germinal cells. The above findings reported in this article have not been cited in any previous studies and are suggesting that the kidney tonifying formula may act through the mechanism of promoting body immune function, metabolism and biotransformation, and, therefore, result in anti-aging.