Cratoxylum formosum is an edible plant that is commonly consumed among the people in Northeast Thailand. This study aimed to investigate the gastroprotective effect of the ethanolic extract of C. formosum leaves (C. formosum ethanolic extract [CFE]). Gastric ulceration was induced in Wistar male rats by oral administration of acid/alcohol. Oral dosing with CFE at 250 and 500 mg/kg of body weight after the acid/alcohol induction significantly decreased the number of bleeding spots, area of bleeding, ulcer score, and ulcer index. Pretreatment with 500 mg/kg CFE significantly prevented the gastric damage. Histological studies of the acid/alcohol-induced animals indicated the gastric inflammation with lesion depth through the mucosal layer. Whereas the gastric lesion of the CFE-treated animals at both 250 and 500 mg/kg doses was decreased to be one-fourth of the mucosal layers, pretreatment with 500 mg/kg CFE prior to acid/alcohol induction completely protected against the mucosal damage. Biochemical analysis of gastric mucosa revealed a significant decrease of malondialdehyde in the CFE-treated group in a dose-response manner. These findings suggest that the gastroprotective activity of CFE could be mediated possibly through its antioxidant effect.