Objective：To investigate the relationship of mitochondrial DNA 4977 bp (mtDNA 4977) deletion in the peripheral blood with severity and stability of coronary atherosclerosis. Methods：We selected 90 unrelated patients with coronary atherosclerotic heart disease (CAD) who were diagnosed by coronary angiography (CAG). The severity of pathological changes of the coronary artery was assessed by the number of diseased coronary branches and Gensini score. The CAD patients were further divided into subgroups according to the clinical types, the number of diseased coronary branches and Gensini score. Control group included 60 healthy age-matched subjects. The relative amount of mtDNA 4977 deletion was determined using a nested polymerase chain reaction (PCR) protocol. White blood cell (WBC) count, high sensitive C reactive protein (hsCRP), lipids (TC, TG, LDL-C, HDL-C), plasma glucose (FPG, 2hPG), blood pressure (SBP, DBP) and body mass index (BMI) were all measured. The information on age, sex and medical histories, including smoking status, hypertension and diabetes mellitus,were obtained in all subjects. Clinical parameters, biochemical indicators, the incidence and relative amount of mtDNA 4977 deletion were compared between the subgroups; the correlation coefficients of mtDNA 4977 relative amount with WBC count, hsCRP and other conventional risk factors for CAD were calculated. Results：The incidence and relative amount of mtDNA 4977 deletion in the peripheral blood in CAD patients were significantly higher than those in the controls (P＜0.01). No significant differences were found in the incidence and relative amount of mtDNA 4977 deletion between patients with angina pectoris and acute myocardial infarction (P＞0.05). MtDNA 4977 deletion incidence and relative amount increased with the increase of diseased coronary branches and Gensini score.In CAD patients mtDNA 4977 deletion relative amount was positively correlated with the number of diseased coronary branches and Gensini score(P＜0.01), not correlated with WBC count and hsCRP. Conclusion: Peripheral blood mtDNA 4977 deletion can be used to predict the severity of coronary atherosclerosis, though it is not associated with the stability of pathological changes of the coronary artery.