Abstract: Objective: To study the relationship between the endometrial carcinoma in young woman and the polycystic ovary. Methods: A total of 15 young women with endometrial carcinoma were included in this study, the thickness of endometrium was measured with ultrasound (double- layer method); The length and width of ovary were measured, the ovarian volume was calculated with the formula of π/6 X length X width²; Pathological examinations were performed after operation. Results: Among the 15 cases with endometrial carcinoma, 11 were polycystic ovary (73.3%), the ovarian volume was increased significantly in both sides (average ovarian volume was 22.94cm³), which was 3.55 times bigger than normal ovary; However, the average endometrial thickness was 2.35 cm, which was about 2 times thicker than normal endometrium. All of 11 PCO cases had irregular menstruation, 8 of them had been treated with hormone repeatedly (72.7%). Conclusions: The increase of endometrial thickness caused by endogenous estrogen and extragenous estrogen in patients with polycystic ovary is the high risk factor for endometrial carcinoma in young woman.