Aim To preliminarily explore the diagnostic value and usefulness for risk stratification of myeloperoxidase(MPO) plasma levels in patients with acute coronary syndrome(ACS). Methods Eighty patients who underwent coronary angiography were enrolled in this study.They were divided into three groups: ACS group(n=27), SAP group(n=27) and the control group(n=26).Blood samples were taken from the artery before angiography in all patients.Each subject was sought in details of history of hypertension,hyperlipidemia,diabetes and smoking habits.The efficacy of therapy,the cardiovascular events(myocardial infarction,the need for revascularization,or death) were recorded after 6 months of follow-up. The concentrations of MPO were measured by enzyme-linked immunosorbent assays(ELISA). Results Median plasma MPO level in ACS group(30.26±30.65 μg/L) was significantly higher than that in SAP group(15.00±11.36 μg/L) and the control group(14.34±9.25 μg/L)(p<0.001),and median plasma MPO level in patients of SAP group and the control group were not significantly different(P=0.73).Median plasma MPO level in patients with acute myocardial infarction(AMI)and unstable angina(UA) were not significantly different(p<0.05).There is no obvious correlation between the levels of plasma MPO and the serum levels of cTnI,hs-CRP,the prevalence of the 4 major risk factors for CHD.Multivariate logistic regression analysis showed that plasma MPO level,fasting plasma glucose and sex were the significant variaties and independent between the patients with ACS,SAP and the control subjects,the plasma MPO level is the most important variables(OR=16.92).The risk for subsequent cardiovascular events is higher in the paitents with elevated level of MPO(>49.89 μg/L,90~(th) percentile of MPO distribution). Conclusions Plasma MPO maybe a new risk biomarker for ACS.MPO plasma levels powerfully predict an increased risk for subsequent cardiovascular events.