Phellamurin, a flavonoid isolated from the leaves of Phellodendron amurense (Rutaceae), has not yet been investigated for its effects on the gastrointestinal tract. In this study, we evaluated its gastroprotective potential using an HCl/ethanol-induced gastric mucosal injury model in rats and an oxidative stress model in primary cultured rat gastric mucosal cells. Oral administration of phellamurin significantly reduced gastric lesion areas. Phellamurin also protected gastric mucosal cells against hydrogen peroxide (H₂O₂)-induced oxidative stress at concentrations that did not show detectable cytotoxicity under the present assay conditions. Quantitative PCR analysis showed no significant changes in the expression levels of antioxidant-related genes or cyclooxygenase (COX) genes. Phellamurin moderately inhibited Helicobacter pylori growth at 1 mM but did not inhibit urease activity. These findings suggest that phellamurin exerts gastroprotective effects, possibly through antioxidant-related cytoprotective mechanisms, rather than through direct antibacterial or urease-inhibitory activity.