CONTEXT: Gastric ulcer is a common gastrointestinal disorder with increasing incidence and prevalence attributed to loss of balance between aggressive and protective factors. Nobiletin (NOB), a major component of polymethoxyflavones in citrus fruits, has a broad spectrum of health beneficial properties including anti-inflammatory and anti-tumor activities. Although NOB was originally shown to possess anti-inflammatory activity, its effects on gastric ulcer were rarely explored previously. OBJECTIVE: The aim of the present study was to investigate the anti-ulcerogenic activity of NOB on ethanol-induced gastric ulcer in mice and to elucidate the underlying mechanisms. METHODS: Seventy-two male Kunming mice administered with absolute ethanol (0.2 ml/animal) were pretreated with NOB (5, 10 or 20 mg/kg), cimetidine (100 mg/kg), or vehicles by intragastric administration in different experimental groups for three days, and animals were euthanized 3 h after ethanol ingestion. Gross and microscopic lesions, immunological and biochemical parameters were taken into consideration. RESULTS: The results showed that ethanol induced gastric injury, increased malondialdehyde (MDA) levels, decreased glutathione (GSH) content, superoxide dismutase (SOD) activity, and prostaglandin E (PGE) levels, increased pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) levels and myeloperoxidase (MPO) activity, as well as the expression MAPK signaling pathway. Pretreatment with NOB significantly attenuated the gastric lesions as compared to the ethanol group. CONCLUSIONS: These findings suggest that the gastroprotective activity is attribute to the improvement of antioxidant activities, the stimulation of PGE, and the reduction of pro-inflammatory cytokines through the MAPK pathway.