We evaluated the qualitative chemical composition and tested the antiulcer actions on cold/restraint stress ulcers, the healing effect on chronic acetic acid-induced gastric ulcers, and thein vivoandin vitroantioxidant capacity ofOcimum suaveextract. Triterpenes, flavonoids, sugars, phenols, sterols, and multiple bonds were among the phytochemicals detected. The extract (250–500 mg/kg) dose-dependently inhibited the formation of gastric ulcers induced by cold/restraint stress (52.30%–83.10%). The prophylactic actions were associated with significant increases in gastric mucus production. There was significant histological healing of chronic ulcers following 14-day treatment withO. suaveextract (250–500 mg/kg). We also evaluated the efficacy ofO. suaveextract in cold/restraint-induced oxidative stress in rat stomach tissue.O. suave(500 mg/kg) ameliorated the decreased levels of reduced glutathione from 0.85 (control group) to 2.08 nmol/g tissue. The levels of SOD and catalase were also improved in rats treated withO. suaveextract. The extract had a high phenol content (899.87 mg phenol/g catechin equivalent),in vitroDPPH radical scavenging activity (89.29%), and FRAP (antioxidant capacity) (212.64 mg/g catechin equivalent). The cytoprotective and ulcer healing effects of the extract are attributed to enhanced mucus production and the antioxidant properties which may likely be associated with the high presence of flavonoids and polyphenols.