Background-The evidence supporting the use of beta-blockers in patients with acute coronary syndrome after successful percutaneous coronary intervention has been inconsistent and scarce. Methods and Results-Between March 1, 2009, and December 30, 2014, a total of 3180 eligible patients with acute coronary syndrome undergoing percutaneous coronary intervention were consecutively enrolled. The primary end point was all-cause death and the secondary end point was a composite of all-cause death, nonfatal myocardial infarction, heart failure readmission, and cardiogenic hospitalization. Patients were compared according to the use of beta-blockers at discharge. Compared with the no beta-blocker group, the risk of all-cause death was significantly lower in the beta-blocker group (hazard ratio [HR], 0.33; 95% CI, 0.170.65 [P=0.001]). A consistent result was obtained in multiple adjusted model and propensity scorematched analysis. The use of beta-blockers was also associated with decreased risk of composite of adverse cardiovascular events (HR, 0.47; 95% CI, 0.280.81 [P=0.006]), although statistical significance disappeared after multivariable adjustment and propensity score matching. Furthermore, we performed post hoc analysis for the subsets of patients and the results revealed that patients with nonST-segment elevation myocardial infarction benefited the most from beta-blocker therapy at discharge (HR, 0.04; 95% CI, 0.000.27 [P=0.001]), and the use of <50% of target dose was significantly associated with better outcome compared with no beta-blocker use, rather than >= 50% of target dose. Conclusions The administration of relatively low beta-blocker dose is associated with improved clinical outcomes among patients with acute coronary syndrome after successful percutaneous coronary intervention, especially for patients with non-ST-segment elevation myocardial infarction.