The gastroprotective effects of BST-104 (a water extract of Lonicera japonica) and the mechanisms involved were investigated in murine models of gastritis and peptic ulcer. The gastroprotective effects of BST-104 and its active components were evaluated in rat models of HCl/ethanol-induced gastritis and acetic acid-induced gastric ulcer. After orally administering BST-104, chlorogenic acid, rebamipide (positive control), or vehicle to each animal model, gastric lesion sizes, gastric mucus statuses, proinflammatory cytokine levels, and oxidative stress were measured. Superoxide dismutase (SOD), catalase, and malondialdehyde (MDA) levels and oxidized/reduced glutathione (GSH) ratios in gastric mucosal tissues were measured to evaluate oxidative stress. To clarify the action mechanism of BST-104, we investigated nuclear factor (NF)-κB pathway involvement by real-time polymerase chain reaction (PCR). In the acetic acid-induced ulcer model, oral administration of BST-104 at 50, 100, or 200 mg/kg significantly reduced gastric lesions by 38%, 43%, and 55%, respectively, compared with vehicle controls. BST-104 significantly increased gastric mucus contents and this was accompanied by higher levels of hexosamine, sialic acid, and prostaglandin E in gastric mucus. Furthermore, BST-104 treatment increased antioxidant activities, as evidenced by higher levels of catalase, SOD, and oxidized/reduced GSH and lower MDA levels. In addition, BST-104 significantly suppressed proinflammatory cytokine (tumor necrosis factor-α, interleukin [IL]-6, and IL-1β) increases, and real-time PCR showed that BST-104 significantly downregulated NF-κB expression. In summary, BST-104 and its active component, chlorogenic acid, were found to have gastroprotective effects by virtue of their antioxidant and anti-inflammatory properties through downregulation of NF-κB expression.