['To explore the expression change of ER-α36 in endometria of PCOS patients.', 'Proliferative endometria were collected and divided into three groups: CE group (n=30), proliferative endometria from control women; PCOSE group (n=30), proliferative endometria from PCOS patients; HPCOSE group (n=15), hyperplastic endometria from PCOS patients. The cellular localization of ER-α36 and ER-α66 was analyzed by immunohistochemistry, and expression of ER-α36 and ER-α66 was determined by immunohistochemistry and Real-Time Quantitative PCR. The correlation between serum hormone concentration and expression of ER-α36 and ER-α66 was analyzed.', 'ER-α36 was localized on the cell surface, cytoplasm and nucleus of glandular epithelial cells of both CE and PCOSE groups, mainly on the cell surface, and ER-α66 was localized on the nucleus. The protein and mRNA expression of ER-α36 was decreased from CE, PCOSE to HPCOSE group, while expression of ER-α66 showed no obvious difference among groups. The expression ratio of ER-α36 to ER-α66 of CE, PCOSE and HPCOSE group showed a decreasing tendency. The expression of ER-α36 and its expressive ratio to ER-α66 was negatively correlated with serum concentration of LH, LH/FSH, testosterone and androstenedione.'] Is lower expression of ER-α36 associated with the development of endometrial hyperplasia in PCOS patients?