SummaryBackground: equine gastric ulcer syndrome (EGUS) has a multifactorial nature and it affects both the squamous and glandular mucosa of the stomach. Multiple therapeutic strategies involving large periods of medication are used to treat this condition. Objective: to evaluate the effects of administering corn oil (CO) to horses with induced gastric ulcers, and to describe the mechanism of action of the mucosal repair. Methods: fifteen horses divided into three groups were used. A combination of confinement and phenylbutazone was used during the ulcer-induction phase. After the gastroscopic evaluation and laboratory tests, animals were treated with sucralfate (SA; group I), and CO at doses of 70 and 90 mL/100 Kg (groups II and III, respectively). Gastroscopy, gastric content collection, and biopsy of the glandular mucosa were performed to analyze prostaglandin E 2 (PGE 2 ), pH, and antioxidant and oxidant parameters. Results: mild to moderate gastric lesions were induced in the glandular and non-glandular mucosa. Among the mechanisms of the treatments, reestablishment of the antioxidant parameters and inhibition of myeloperoxidase (MPO) oxidant enzyme were prominent, but PGE 2 concentration had a weak influence. Conclusion: similarly to SA, CO only had therapeutic effects in the glandular mucosa.