Background: There had been few evidences supporting the proper timing of bronchoscopy in uencing on clinical outcomes including mortality in mechanically ventilated patients with aspiration pneumonia. Method: Mechanically ventilated patients with aspiration pneumonia in medical intensive care unit at tertiary hospital from March 2003 to December 2013 were retrospectively reviewed. All of pneumonias were confi rmed by historical and clinical probability with defi nite fi ndings of chest computed tomography compatible with aspiration. By defi nition, patients who were done bronchoscopy within 24 hours after intubation werecategorized as early bronchoscopy group. We compared demographics, clinical parameters and outcomes including mortality between two groups. Results: 182 patients were diagnosed as aspiration pneumonia with their probability. Early group (n=93) showed no signifi cant differences in demographic features including acute physiology and chronic health evaluation II scores compared with late group. Early group showed signifi cant lower in-ICU mortality and in-hospital mortality (6.5 vs. 26.1% and 10.8 vs. 33.0%, P<0.001, respectively) regardless of the appropriateness of proper antibiotics. In addition, their sequential organ failure assessment score and clinical pulmonary infection score on day 7 tended to decrease more rapidly. Patients in early bronchoscopy group had been extubated more successfully, and showed shorter length of mechanical ventilation and stay in ICU. Interestingly, they had more previous aspirationhistory, be done brochoscopy frequently, and admitted on weekday rather than holiday or weekend. Cox regression analysis showed only the early timing of bronchoscopy was associated with lower 90 day mortality (Odds ratio, 0.261; 95% CI, 0.111-0.613). Conclusions: Early bronchoscopy could result in more benefi cial effect on clinical outcomes in mechanically ventilated patients with aspiration pneumonia.