Annickia affinis is a medicinal plant traditionally used in Africa against several diseases including peptic ulcers. We conducted this study to evaluate the antiulcer and gastroprotective activities of the ethanolic extract of the stem bark of this plant. The antiulcer activity was evaluated on Wistar rats using 95% ethanol and then administering to them as treatment solutions, the ethanolic extract of the stem bark of the plant and other referenced anti-ulcer drugs over periods of 7 and 14 days. The gastroprotective activity was carried out following the opposite path, the different batches of rats first received one of the treating solutions and an hour later, the ulcer was induced on them and they were finally sacrificed an hour after administring the ulcerogenic solution for the macroscopic and microscopic analysis of their stomachs. Phytochemical screening revealed the presence of alkaloids, saponins, reducing sugars, coumarins, anthocyanins, anthraquinones. UPLC-MS analysis revealed the presence of 16 compounds, notably berberine, berberrubine, canadine, palmatine, jatrorrhizine, columbamine, pseudocolumbamine, 7,8-dihydro-8-hydroxypalmatine, atherosperminine, argentinine, 7-hydroxydehydronuciferine, 7-hydroxydehydronornucierine, Caryophyllene oxide, 1,5-epoxysalvial-4(14)-ene, humulene epoxide II and spathalenol. The administration of the ethanolic extract of the stem bark of Annickia affinis at doses of 2000 mg/kg and 5000 mg/kg showed no acute toxicity. The results obtained from the evaluation of pharmacological activities revealed that the ethanolic extract of the stem bark of Annickia affinis would have antiulcer and gastroprotective properties comparable to omeprazole and sucralfate at the dose of 150 mg/kg. It appears from this study that the stem bark Annickia affinis could be used both in the prevention and in the treatment of gastric ulcers which would justify its use in the traditional pharmacopoeia.