Abstract: ObjectiveTo explore the association between reproductive factors and breast cancer.MethodsA matched case-control study was conducted from May 2007 to Apr 2008 Overall 119 new diagnosed breast cancer patients in Sichuan Cancer Hospital and 119 health female physical exanainees matched with age were enrolled in the study Reproductive and menstrual factors were investigated with a questionnaire.The data were processed with EPI data 3.0 software, and conditional and un-conditional logistic regression analysis were conducted with EPI Info 2002 software. Results The major risk factor of breast cancer for the cases was the number of miscarriage≥3 (OR=6.10, 95% CI=1.79-20.76, conditional logistic regression).In pre-menopausal sub-group, the OR (95% CI) of the number of miscarriage ≥3 was 4.69(1.10-19.91, unconditional logistic regression).Taking estrogen more than one year was another risk factor for breast cancer in pre-menopausal sub-group (OR=3.69, 95% CI=1.12-12.15, unconditional logistic regression).ConclusionMiscarriage may increase the risk of breast cancer, and taking estrogenic dnzg may increase the risk of breast cancer in pre-menopausal women.