The anti-ulcerogenic properties of plantain banana have been well established even though the active ingredient has only recently been identified as the flavonoid leucocyanidin. The aim of this study was to evaluate the ability of the natural flavonoid leucocyanidin and synthetic analogues to protect the gastric mucosa against aspirin challenge. Natural and synthetic flavonoids were added to the diet of rats, and their anti-ulcerogenic potential evaluated using a prophylactic animal model. Leucocyanidin and its synthetic hydroxyethylated and tetrallyl derivatives were found to protect the gastric mucosa from aspirin-induced erosions. Leucocyanidin and its hydroxyethylated and tetraallyl derivatives significantly increased mucus thickness. Whilst the mechanism by which the natural and synthetic flavonoids protect the gastric mucosa remains to be fully elucidated, it may, as indicated in this study, involve an increase in mucus thickness.