The general restenosis rate after emergent coronary stent implantation for ST-elevation myocardial infarction (STEMI) patients in Japan has yet to be fully established. Totally 696 STEMI patients without left main disease were enrolled for either ASPARAGUS (22 centers) or VAMPIRE (23 centers) trial. Out of these, 202 lesions in 202 patients with baseline and 6-month follow-up quantitative coronary angiography (QCA) data after emergent bare metal stent (BMS) implantation without either aspiration or distal protection devices were enrolled for this study. QCA was performed at an independent core laboratory. Minimal lumen diameter (MLD), reference diameter (RD) and diameter stenosis (DS) were estimated at pre, post and follow-up phase. Left ventricular ejection fraction was evaluated by quantitative left ventriculography. Six-month binary restenosis (DS >50%) rate and target lesion revascularization (TLR) were investigated. Six-month binary restenosis and TLR was found in 39 (19.3%) and 32 (18.6%), respectively. In the patients with binary restenosis, smaller pre-RD (2.46 ± 0.54 vs. 2.68 ± 0.73 mm, p = 0.03), post-MLD (2.08 ± 0.54 vs. 2.34 ± 0.52 mm, p = 0.009), acute gain (1.90 ± 0.49 vs. 2.13 ± 0.61 mm, p = 0.001) and follow-up RD (2.44 ± 0.67 vs. 2.71 ± 0.63 mm, p = 0.03) were observed. When the lesions are divided into quartiles of pre-RD (≤2.16, 2.18-2.61, 2.62-3.11, ≥3.12 mm), the binary restenosis rates were 26, 25.5, 16 and 10%, and TLR rate were 19.5, 29.6, 13.6 and 12%, respectively. RD was smaller at pre and follow-up than post phase (pre: 2.64 ± 0.71 mm; post: 2.89 ± 0.57 mm; follow-up: 2.66 ± 0.64 mm; pre vs. post: p < 0.001; post vs. follow-up: p = 0.001; pre vs. follow-up: p = 1.00). In this study cohort, the binary restenosis and TLR rate were considerable in patients with BMS for STEMI. The decrement of RD at follow-up period was common and it indicates that vessel shrinkage post PCI for acute myocardial infarction may be a myth. TLR rate was more than the binary restenosis rate in two quartiles of pre-RD. Robust guideline regarding stent type and revascularization for STEMI patients should be established.