Women with polycystic ovary syndrome (PCOS) exhibit a lower pregnancy rate, which may be related to decreased estrogen receptor (ER) expression or endometrial receptivity. We measured expression of ERα, ERß and the novel G protein-coupled ER (GPR30) in endometrium during window of implantation (WOI) in PCOS patients. Fifteen Chinese women with PCOS were compared to 15 normal subjects. Serial trans-vaginal ultrasonic scanner (TVUS) examinations detected follicular development, and endometrial thickness and pattern were assessed via TVUS on the day of ovulation. GPR30 expression was detected in the cytoplasm of endometrial epithelial cells, and was significantly lower in the PCOS group (p0.05), but there was a significant difference in the ultrasonic pattern (p<0.05). Endometrial expression of GPR30, ERα and ERß was decreased during WOI in PCOS patients, and was accompanied by poor endometrial receptivity, low pregnancy rate and higher spontaneous abortions. We propose that restored receptor expression might improve endometrial receptivity and help lower infertility associated with PCOS.