Abstract: Aromatase cytochrome p450, encoded by the Cytochrome P450 19 （CYP19） gene, is a key enzyme in estradiol biosynthesis, which catalyzes the conversion of androstenedione and testosterone to estrone and estradiol, respectively. P450arom exists in many normal tissues such as ovary, fat and adrenal gland. The CYP19 gene codes for aromatase. Its tissue specificity determines the physical or pathological effects of P450arom in different tissues. The hyperfunction of CYP19 gene leads to the increase of its product P450arom, which induces occurrence and development in many estrogen dependent diseases such as endometrial carcinoma, endometriosis, breast cancer; the insufficiency of CYP19 gene leads to the accumulation of its upper substrate androgen, which can be observed in polycystic ovary syndrome（PCOS）. Now summarize the structure, adjusting mechanisms of CYP19 and the relationship between CYP19 and estrogen dependent diseases, PCOS. Meanwhile put forward prospects towards basic researches and clinic treatments of these dieases.

Key words: Aromatase, Cytochrome P-450 enzyme system, Estrogens, Neoplasms, hormore-dependent, Polycystic ovary syndrome