P>Objective Insulin resistance is a possible cause of polycystic ovary syndrome (PCOS). It is presumed that ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) is associated with insulin resistance. The purpose of this study is to explore the expression of ENPP1 in granulosa cells of the ovary and its relationship with PCOS. Methods Twelve aliquots of follicular granulosa cells were isolated from 12 samples of the patients with PCOS and 22 aliquots from 22 samples of the patients without PCOS, respectively．ENPP1 expression was analyzed by reverse transcription polymerase chain reaction (RT-PCR ) and in situ hybridization. The relative expression of ENPP1 mRNA was detected by realtime quantitative polymerase chain reaction (realtime PCR). Results ENPP1 was expressed in granulosa cells of the ovary. ENPP1 expres