Background: In high-performance horses, it is reported that 50 to 90% have stomach disorders, especially gastritis and gastric ulceration, which compromises both, athletic performances, and health status. This work aims to stablish changes in gastric pH and gastrin hormone in horses submitted to general inhalation anesthesia and in supine position, to determine the occurrence of duodenogastric and gastroesophageal reflux. Eight mares fasted for eight hours, subjected to inhaled anesthesia and in supine position were monitored during the anesthetic period. Gastric pH, arterial blood gases and vital signs data were recorded.Results: In the post-anesthetic period, gastric pH was evaluated for 24 h, samples were collected at one-hour intervals. In addition, blood samples were collected for gastrin hormone evaluation before the anesthetic procedure (8-hour fast), during the anesthetic recovery period, and four months after the anesthetic procedure, 90 minutes after the morning meal. Gastric pH during the anesthetic period remained within physiological values (mean value 4.52 ± 1.69), without changes between times (p > 0.05). After anesthesia, mean gastric pH values increased, remaining alkaline during the 24 h of evaluation, differences between T0 (4.88±2.38), T5 (7.08±0.89), T8 (7,43±0,22), T9(7,28±0,36), T11 (7.26±0.71), T13 (6.74±0.90), and T17 (6.94±1.04) (p < 0.05) were observed. There was an increase in gastrin hormone in the post-anesthetic period (20.15±7.65 pg/ml) compared to baseline (15.15±3.82 pg/ml) (p < 0.05). Conclusions: The results obtained demonstrate that general inhalational anesthesia and dorsal decubitus in horses, for 90 min, promotes gastric pH alkalinization for 24hours after anesthesia, possibly induced by entero-gastric reflux. Therefore, gastric mucosa protectors should be considered preventively when horses are submitted to general anesthesia and supine.