Abstract: Objective To investigate the association between type 2 diabetes mellitus and breast cancer in Han population in China.Methods A non-matched case-control study,which included 400 female breast cancer patients from Tumor Hospital of Heilongjiang Province.They all had been operated and their pathology slides were diagnosed as primary breast cancer.And the 400 female who went for check up in Heilongjiang Electric Power Hospital were selected as controls.All subjects were interviewed with a questionnaire and detected for fasting plasma glucose.Chi-square test,U-test and logistic regression analysis were then performed.Results The results of single-factor logistic regression showed that type 2 diabetes mellitus was the risk factors of breast cancer odds ratioOR=6.204,95% confidence interval95%CI:3.008-12.799).After adjustment for age,type 2 diabetes mellitus was the risk factor of breast cancer(OR=6.019,95%CI:2.903-12.476).Adjustment for age,education background,power of work,financial reward,smoking,drinking,physical exercises,elder age at first live birth,having the history of abortion,and mental depression,type 2 diabetes mellitus was still the risk factor of breast cancer(OR=3.912,95%CI=1.526-10.028).Conclusion Type 2 diabetes mellitus was associated with the breast cancer.