Abstract: CYP11A encoding cholesterol side-chain-cleavage-enzyme P450scc is the key to the synthesis of steroid hormones initial and rate-limiting enzyme，which exits in almost all animals and plants. CYP11A is regulated by hormone levels and self-regulation of the promoter region of certain structures. The certain part of a pentanucleotide repeat（TTTTA）n in its promoter may be related to transcriptional activity and gene expression. Polycystic ovary
syndrome（PCOS） is a very common female reproductive endocrine disease，hyperandrogenism is the main feature of PCOS. CYP11A is one of the important genetic susceptibilities. Its role in the pathogenesis of PCOS is still controversial， whicn has not been fully clarified and is worth further study.

Key words: Cholesterol side-chain cleavage enzyme, Cytochrome P-450 enzyme system, Polycystic ovary syndrome, Genes, Gene expression