Excimer laser coronary angioplasty (ELCA) is a unique revascularization modality that can vaporize plaque and thrombus. Compared to thrombus aspiration therapy, ELCA is reported to provide better microcirculation and reduced peripheral embolism in treatment for acute coronary syndrome. Excimer laser catheters come in various sizes, and we sought to compare the 0.9-and 1.4-mm-diameter catheters. We retrospectively enrolled 90 acute myocardial infarction (AMI) patients who underwent primary percutaneous coronary intervention with excimer laser from August 2013 to March 2017 in our hospital. Patients were grouped by diameter of catheter that had been used, the 0.9 mm group (n = 51) and 1.4 mm group (n = 39). We evaluated myocardial perfusion, procedural success rate, short-term outcome, lesion crossability, and complications between the two groups. The percentage of patients whose final thrombolysis in myocardial infarction (TIMI) grade was 3 (0.9 mm 86.3% vs 1.4 mm 89.7% p = 0.75) and final myocardial blush grade (MBG) was 3 (0.9 mm 72.5% vs 1.4 mm 69.2% p = 0.82) was similarly high for both groups. Procedural success rate, in-hospital major adverse cardiac events (MACE), lesion crossability, and complications were also similar. This study showed that efficacy of 0.9 and 1.4 mm excimer laser catheter was equivalent in ELCA for AMI patients. If one takes into account lesion crossability, debulking effects, and the stunned platelets phenomenon, the 0.9 mm excimer laser catheter is sufficient for ELCA in AMI patients.