Abstract: OBJECTIVE To observe the therapeutic effect of Sanjiezhitong cataplasm on hyperplasia of mammary glands in rats, and to explore its mechanism. METHODS The model of mammary hyperplasia was established with i.m. injection of estradiol benzoate and progesterone per day, and the administration time was 30 d. The morphologic changes of nipple were recorded, the levels of serum sex hormone were determined by radio immunoassay and the morphologic change ofpathological tissue of mammary gland were observed. RESULTS Sanjiezhitong cataplasm could remarkably reduce the nipple height and efficiently decrease the level of estradiol and increase the level of progesterone. Histopathology examination showed that Sanjiezhitong cataplasm could decrease the number of alveolus in lobules of mammary gland, improve the degree of vessel epithelial proliferation, inhibit the secretion of alveolus and lactiferous ducts. CONCLUSION Sanjiezhitong cataplasm have the good therapeutic effect on hyperplasia of mammary glands in rats and can improve the level of sex hormone efficiently.