Purpose Gastritis is found to be one of the most common gastrointestinal diseases worldwide. However, current therapeutic agents cause side effects, interaction, and recurrence. Allantoin has anti-inflammatory and wound healing properties. In this study, the therapeutic effect of allantoin has been assessed on the histopathological indices and gastric mucosal barrier of male rats. Methods Male rats were equally divided into control, ethanol-induced gastritis, and allantoin groups. The therapeutic groups consisted of gastritis plus 12.5 mg/kg allantoin, gastritis plus 25 mg/kg allantoin, and gastritis plus 50 mg/kg allantoin groups. After 5 days of allantoin administration, the rats were sacrificed and a part of their gastric tissue was maintained at −70 °C for prostaglandin E2 (PGE2) and non-protein sulfhydryl (NP-SH) measurements. Another part was stained with hematoxylin and eosin and Masson’s trichrome. Results We found that Allantoin increased parietal and mucosal cell counts and mucosal thickness after gastritis induction. In addition, the number of leukocytes and vessels decreased in both of the mucosal and the submucosal layers. Allatoin improved gastric ulcer in all treatment groups. Gastric levels of PGE2 and NP-SH increased after allantoin treatment. Conclusion This study indicated that allantoin had a considerable effect on gastritis treatment, which seems to result from the reinforcement of gastric mucosal barrier.