Abstract: Peripheral blood mitochondrial DNA copy number (mtDNAcn) is a novel biomarker reflecting oxidative stress status in body. Emerging epidemiological evidences have reported associations of peripheral blood mtDNAcn with major chronic diseases such as cardiovascular diseases, Parkinson's disease, and cancer. It is of great importance to develop methods for measuring peripheral blood mtDNAcn and to identify their risk factors, which could help to promote prevention of chronic diseases. In this study, we introduce detection methods of mtDNAcn and give an outline review on the potential influencing factors of peripheral blood mtDNAcn, aiming to present evidences for identification of peripheral blood mtDNAcn as an early biomarker and to provide technical support for the prevention of chronic diseases.