The present study investigated the gastroprotective effects of a cinnamon diet using different gastric ulcer mouse models. Dose dependency and the effective dose period of administration of a cinnamon powder diet were established using the water immersion stress gastric ulcer model. A cinnamon powder diet significantly protected mice against ulceration by stress, ethanol, HCl and oral administration of aspirin, but not against ulceration by oral administration of indomethacin or subcutaneous administration of indomethacin or aspirin. Such a diet conferred protection against gastric ulcers at an effective concentration of 100 mg cinnamon powder per gram of food after administration for 4 weeks and the active compound of cinnamon powder for gastroprotective activity was identified as cinnamaldehyde. These findings indicate that regular ingestion of cinnamon powder offers gastroprotection presumably through a cytoprotective mechanism but the efficacy against NSAIDs-induced gastric ulcers may be limited.