We aimed to determine the effect of aortic annular enlargement on the mid-term outcomes of aortic valve replacement surgery by comparing patients with the same-sized (≤23 mm) native aortic annuli. From January 2011 to June 2022, 1,328 patients underwent isolated aortic valve replacement-1,163 without aortic annular enlargement (AVR group) and 165 with aortic annular enlargement (AVR+AAE group). Propensity score matching identified 112 pairs, controlling for native aortic annulus diameter, age, sex, diabetes, chronic lung disease, dialysis, ejection fraction, prior cardiac surgery, indication, hypertension, dyslipidemia, valve type, prior stroke, prior myocardial infarction, and case status. Demographic and preoperative parameters were similar, except body surface area was larger in the AVR+AAE group (2.1 m2 vs 1.9 m2). Median native aortic annulus diameter was 23 mm in both groups. Median prosthesis size was 25 and 23 in the AVR+AAE and AVR groups, respectively. The AVR+AAE group had longer cardiopulmonary bypass (143 vs 111 mins) and cross-clamp (115 vs 82 mins) times. Incidences of perioperative complications including operative mortality (1.8% AVR+AAE vs 3.6% AVR) were similar between groups. 6-year survival was 98% in the AVR+AAE group and 74% in the AVR group (p=0.016). Aortic annular enlargement was an independent protective factor for mid-term mortality with a hazard ratio of 0.19 (p=0.006). The rate of moderate/severe patient-prosthesis mismatch was 19% in the AVR+AAE group and 31% in the AVR group (p=0.16). Patients with small native aortic annuli (≤23 mm) undergoing isolated aortic valve replacement may benefit from aortic annular enlargement.