Objective To evaluate the value of mean platelet volume (MPV) in identifying the location of infarct at left circumflex artery (LCX) in patients with non-ST-elevation myocardial infarction (NSTEMI).Methods In this retrospective study,184 consecutive patients with NSTEMI were eligible to be enrolled from January 1,2009 to June 30,2011 and laboratory examinations including platelet count,B-type natriuretic peptide (BNP),troponins test (TnI),C-reactive protein and serum creatinine (SCr) were done.The demographics and detailed history of patients were documented.In addition,left ventricular ejection fraction (LVEF) test and coronary angiography to determine the culprit vessel implicating in infarction were carried out in all enrolled patients.The patients were categorized into LCX group and N-LCX group according to culprit vessel.Results Of 184 patients,68 patients were in LCX group and 116 patients had left anterior descending artery (LAD) lesion or right coronary artery (RCA) lesion.High percent of LCX infarction were found in patients with high MPV level and low BNP level,and in smokers.And lower proportion of those patients had previous percutaneous coronary artery intervention.The results showed that MPV was larger in patients with LCX infarction than that in patients with LAD or RCA.Receiver operating characteristic curve showed the area under curve was 0.75 (95％ CI:0.675-0.826).An optimized cut off point at 9.15 fL of MPV showed 83.8％ sensitivity and 63.8％ specificity for prediction of LCX infarction.Multivariate analysis also showed that MPV was the only independent predictor of a LCX infarction in patients with NSTEMI [OR=1.32,(95％ CI:1.031-1.688),P＜0.05].Conclusions MPV was the only independent factor associated with LCX infarction in patients with NSTEMI.