Studies have proven that alkaline water has a protective effect on gastric diseases. However, the underlying mechanism is not clear. Moreover, in some countries, especially in China, purified water (distilled water) is also an important form of drinking water, while its protective effect on gastric diseases is still unknown. This study aimed to compare the effects of distilled water (pH = 5.6 ± 0.3) and alkaline natural mineral water (pH = 9.3 ± 0.6) on ethanol-induced gastric ulcers in mice and to further clarify the underlying mechanisms. Pepsin activity, prostaglandin E-2 (PGE2) and heat shock protein 70 (HSP70), superoxide dismutase (SOD), reduced glutathione (GSH), and malondialdehyde (MDA), as well as the oxidative stress pathway related proteins such as nuclear factor erythroid-2 related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and NADH quinone oxidoreductase 1 (NQO1) were measured. After alkaline natural mineral water treatment, the levels of PGE2 and HSP70 were significantly increased (p < 0.05). Antioxidant indexes (SOD, GSH, and MDA) and Western blot results (Nrf2, HO-1, and NQO1) showed that alkaline natural mineral water did not alleviate gastric ulcers by improving oxidative stress. Pepsin activity assay displayed that the pepsin activity was significantly declined after alkaline natural mineral water treatment compared with the distilled water treatment (p < 0.05). This study indicated that alkaline natural mineral water may alleviate the ethanol-induced gastric ulcers in mice by inhibiting the pepsin activity and increasing the levels of PGE2 and HSP70.