Background: Circulating endothelial progenitor cells (EPCs) are known to be mobilized after acute myocardial infarction (AMI). We investigated the relation between the EPC mobilization and improvement of left ventricular (LV) function and predictor for EPC mobilization. Methods: A total of 37 patients (63.2짹12.7 years, male 72.1 %) with AMI who underwent percutaneous coronary intervention (PCI) were enrolled. The number of EPC was measured in the peripheral blood before PCI and after 5days of PCI. LV ejection fraction (LVEF) was measured before and after PCI, and at one- month after PCI. According to the mobilization of EPC, patients were divided into 2 groups [group I: mobilized group (n=19), group II: non-mobilized group (n=18)]. Results: The group I was older and had lower N-terminal pro-B-type natriuretic peptide levels (NT-proBNP) than the group II (60.1짹13.7 vs. 69.4짹11.2 years, p=0.030; 1641.0짹3026.5 vs. 1829.7짹1470.7 pg/mL, p=0.039, respectively). Baseline CD45lowCD34+VEGFR2+ cells were higher in the group II than the group I (63.9짹95.7 vs. 273.9짹342.8/10⁶ leukocyte, p=0.021). The change of CD45lowCD34+VEGFR2+ cells were significantly higher in the group I than the group II (305.7짹514.9 vs. -219.6짹320.6/10⁶ leukocyte, p=0,001). Baseline LVEF, post-procedure LVEF, and LVEF at one- month after PCI had no significant differences. In multi-variate analyses, the level of NT-proBNP was an independent predictor of EPC mobilization (OR, 13.36, 95% CI 1.43-124.2, p=0.001). Conclusion: The EPC mobilization after PCI in patients with AMI was not related to the improvement of LVEF during short-term. The level of NT-proBNP was an independent predictor of EPC mobilization in patients with AMI treated with PCI.