Objetive. To determine the influence of corn oil on the volatile fatty acids (VFA) concentrations in the gastric juice in horses with phenylbutazone (PBZ) induced gastric ulcers and Correlate the gastroscopic findings with the VFA concentrations. Materials and methods. 15 horses were allotted in 3 groups. Group I (control) received placebo during first 6 days (induction period) and was treated with sucralfate for 2 weeks (treatment period). Groups II and III received PBZ during the induction phase. After 6 days, horses from group II received 70 mL of corn oil /100 kg of body weight/ po, twice a day, for 2 weeks and horses from group III received 90 mL of corn oil/100 kg of body weight/ po, twice a day, for 2 weeks. All horses were examined by gastroscopy at days 0, 7 and 21. The lesions were recorded and classified according to the number and severity. Samples from gastric fluid were taken to measure the concentrations of the acetic, propionic, butyric and lactic acids. Results. Both PBZ protocols produced lesions in the both non-glandular and glandular areas of the stomach. All the treatments produced healing of the injured mucosa glandular. Neither of the two corn oil treatments affected healing of the gastric ulcers located in the non-glandular area. Conclusions. The concentrations of acetic and butyric acids were highest in the gastric juice. The corn oil and sucralfate did not lead to differences in the concentration of acetic acid and butyric acid.