Background: Gastric inflation (GI) can induce gastric regurgitation and subsequent aspiration pneumonia, which can prolong intensive care unit stay. However, it has not been verified in patients with out-of-hospital cardiac arrest (OHCA). This study aimed to investigate the incidence of GI during prehospital resuscitation and its effect on aspiration pneumonia and resuscitation outcomes in patients with out-of-hospital cardiac arrest. Methods: This was a multicenter, retrospective, observational study. Patients with non-traumatic OHCA aged >19 years who had been admitted to the emergency department were enrolled. Patients who received mouth-to-mouth ventilation during bystander cardiopulmonary resuscitation (CPR) were excluded from the evaluation owing to the possibility of GI following bystander CPR. Patients who experienced cardiac arrest during transportation to the hospital who were treated by the emergency medical service (EMS) personnel, and those with a nasogastric tube at the time of chest or abdominal radiography were also excluded. Radiologists independently reviewed plain chest or abdominal radiographs immediately after resuscitation to identify GI. Chest computed tomography performed within 24 h after return of spontaneous circulation was also reviewed to identify aspiration pneumonia. Results: Of 499 patients included in our analysis, GI occurred in approximately 57% during the prehospital resuscitation process, and its frequency was higher in a bag-valve mask ventilation group (n = 70, 69.3%) than in the chest compression-only cardiopulmonary resuscitation (n = 31, 55.4%), supraglottic airway (n = 180, 53.9%), and endotracheal intubation groups (n = 3, 37.5%) (p = 0.031). GI was inversely associated with initial shockable rhythm (adjusted odds ratio [OR] 0.53; 95% confidence interval [CI]: 0.30–0.94). Aspiration pneumonia was not associated with GI. Survival to hospital discharge and favorable neurologic outcomes were not associated with GI during prehospital resuscitation. Conclusions: GI in patients with OHCA was not associated with the use of different airway management techniques.