<p><b>OBJECTIVE</b>To observe the effect of sequential method of nourishing yin and tonifying yang on serum sex hormone levels in rats with polycystic ovary syndrome (PCOS), and to explore its possible mechanisms.</p><p><b>METHODS</b>PCOS rat models were established by injecting dehydroepiandrosteron (DHEA) subcutaneously. A total of 70 21-day female SD rats were randomly divided into seven groups, ten in each group: the normal control, the model control, the yin nourishing, the yang tonifying, the sequential method, the Westem medicine, and the combined medication. Rats in all groups were treated by gastrogavage for twelve successive days. Serum testosterone (T) and estradiol (E2) were detected by chemoluminescence method. Serum androstenedione (A), follicle stimulating hormone (FSH), luteinizing hormone (LH), insulin (INS), and insulin-like growth factor-I (IGF-I) were detected by radioimmunoassay (RIA).</p><p><b>RESULTS</b>Serum levels of A, T, and E2 were significantly higher in the model control group than in the normal control group (P < 0.05, P < 0.01). Serum levels of A and T were obviously lower in the sequential group than in the model control group with significant difference (P < 0.01). The serum E2 level was obviously lower in the sequential group than in the model control group (P < 0.05). Serum levels of INS and IGF-I were significantly higher in the model control group than in the normal control group (P < 0.05). Serum levels of INS and IGF-I were significantly lower in the sequential group than in the model control group (P < 0.01).</p><p><b>CONCLUSIONS</b>The sequential method of nourishing yin and tonifying yang can lower serum levels of A, T, E2, INS, and IGF-I, and reverse its endocrine disturbance in PCOS rats. One of its mechanisms in decreasing serum levels of A, T, E2 might be possibly through lowering serum levels of INS and IGF-I.</p>