Objective To investigate the association between the proportion of peripheral blood intermediate monocyte subset(Mon2)and prognosis in patients with acute myocardial infarction(AMI)receiving percutaneous coronary intervention(PCI).Methods A total of 100 AMI patients who underwent PCI between March 2021 and June 2022 were enrolled.Peripheral venous blood sam-ples were collected within 24 hours of onset in all patients,and monocyte subsets were analyzed using three-color flow cytometry.Patients were followed up for at least 1 year after discharge,and major ad-verse cardiovascular events(MACE)were recorded.Results The optimal cut-off point for predic-ting MACE occurrence 1 year after PCI in AMI patients based on the Mon2 proportion was 25.65％(area under the curve=0.758,95％CI,0.607 to 0.909,P=0.002),with a sensitivity of 64.3％and a specificity of 86.0％.Patients were divided into high Mon2 proportion group and low Mon2 proportion group according to the optimal cut-off value.There were significant differences in globu-lin,creatinine,fasting blood glucose,left ventricular end-systolic diameter,and Mon2 proportion between the two groups(P＜0.05).After adjusting for potential confounding factors using Cox re-gression,Mon2 proportion was found to be an important indicator for predicting poor prognosis after AMI.Kaplan-Meier survival analysis showed that the Mon2 proportion had a significant impact on the incidence of MACE in AMI patients with different risk stratifications.Conclusion Mon2 can improve the accuracy of predicting MACE after PCI,providing a new perspective for prognostic as-sessment in AMI patients.It is helpful for guiding clinical treatment decisions and improving patient prognosis.