It has been reported that quantitative alterations and sequence variations of mtDNA are associated with the onset and progression of particular types of tumor. However, the relationship between mtDNA content, certain mtDNA polymorphisms in peripheral blood leukocytes and breast cancer risk remain obscure. This study was undertaken to investigate whether mtDNA content and the A10398G polymorphism in peripheral blood leukocytes could be used as risk predictors for breast cancer in Han Chinese women. Blood samples were obtained from a total of 506 breast cancer patients and 520 matched healthy controls. The mtDNA content was measured by using quantitative real-time PCR assay; A10398G polymorphism was determined by PCR-RFLP assay. There was no statistically significant difference between cases and controls in terms of peripheral blood mtDNA content or A10398G polymorphism. However, further analysis suggested that the risk of breast cancer was associated with decreased mtDNA content in premenopausal women (P = 0.001; odds ratio = 0.54; 95% confidence interval, 0.38–0.77), with increased mtDNA content in postmenopausal women (P = 0.027; odds ratio = 1.49; 95% confidence interval, 1.05–2.11). In addition, the associations between mtDNA content and several clinicopathological parameters of cases such as age, menopausal status, and number of pregnancies and live births were observed. This case–control study indicated that the peripheral blood mtDNA content might be a potential biomarker to evaluate the risk of breast cancer for selected Chinese women.