Objective To investigate the expression of apolipoprotein A-Ⅰ (ApoA-Ⅰ) in granulosa cells (GCs) of patients with polycystic ovary syndrome (PCOS). Methods Forty women undergoing in vitro fertilization and embryo transfer were divided into PCOS group (n=20) and control group (n=20), and serum samples on preoperative examination day and GCs samples were collected. The expression of ApoA-Ⅰ protein in GCs was detected by Western blotting, the expression of ApoA-Ⅰ mRNA in GCs was determined by Real-time PCR, and the serum level of ApoA-Ⅰ was measured by immunoturbidimetry. Results The expression of ApoA-Ⅰ protein and mRNA in GCs in PCOS group was significantly lower than that in control group (P＜0.001, P＜0.01), and the serum level of ApoA-Ⅰ in PCOS group was also significantly lower than that in control group (P＜0.05). Conclusion The expression of ApoA-Ⅰ is down-regulated in GCs in patients with PCOS.