Objective To study the value of platelet/lymphocyte ratio(PLR)in predicting coronary artery lesions and their outcome in acute coronary syndrome(ACS)patients after PCI.Methods Three hundred and forty-four elderly ACS patients who underwent PCI and CAG in our hospital from May 2016to August 2018were divided into MACCE group(n=95)and MACCE-free group (n=249).They were further divided into high PLR group(n=247)and low PLR group(n=97) according to the ROC curve for PLR.Their clinical data were analyzed,and the prognostic threshold of PLR was determined according to the ROC curve for PLR and logistic regression analysis respectively.Results The number of smokers was significantly greater,the incidence of DM,serum LDL-C level,PLR and Gensini score were significantly higher in MACCE group than in MACCE-free group(P＜0.01).The area under the ROC curve for PLR in predicting the poor outcome in ACS patients after PCI was 0.898and 0.842respectively(95％CI:0.859-0.937,95％CI:0.794-0.891).The PLR was positively related with the Gensini score(r=0.654,P＜0.01).The incidence of MACCE was significantly higher in high PLR group than in low PLR group(78.35％ vs 7.69％,P＜0.01).High PLR was an independent risk factor for MACCE in elderly ACS patients after PCI(OR=2.527,95％CI:1.058-6.039,P=0.037).Conclusion PLR is related with MACCE in elderly ACS patients after PCI.