Background: G-CSF has a stem cell mobilizing capacity and favorable effects on ventricular remodeling after myocardial infarction. G-CSF based stem cell therapy showed favorable results in animal studies. However the long term outcome of G-CSF based stem cell therapy in clinical trial was remained unknown. We evaluated outcomes of intra-coronary infusion of mobilized peripheral blood stem cells (PBSCs) and mobilization alone by granulocytes – colony stimulating factor (G-CSF) in patients with myocardial infarction. Methods: We compared intra-coronary infusion of the mobilized PBSCs with G-CSF (n=10) and mobilization alone with G-CSF (n=10) in patients with myocardial infarction in MAGIC Cell -1 trial and G-CSF alone (n=6) and control (n=6) in MAGIC Cell-2 trial. Results: At one year follow up evaluation of MAGIC Cell-1 trial, intra-coronary cell infusion improved left ventricular (LV) ejection fraction (48.9 짹 9.0% to 57.4 짹 6.8%, p=0.017) and end-systolic volume (70.3 짹 28.9 mL to 48.4 짹 19.3 mL, p=0.035), but G-CSF alone did not. The cell infusion group showed a significantly better improvement of LV systolic function than the G-CSF alone group (p=0.004). In MAGIC Cell-2 trial, there were no significant differences in LV systolic function and remodeling between the G-CSF and control groups. Patients who received G-CSF administration, especially before stent implantation, showed a modest increase of binary restenosis and a greater late loss of minimal luminal diameter at 6 months follow up compared to the control. Conclusions: Intra-coronary infusion of mobilized PBSCs by G-CSF is better than G-CSF alone. And, G-CSF increases a potential risk of restenosis. Efficacy of Intra-coronary infusion of mobilized PBSCs should be evaluated in large randomized controlled trials.