Acacia seyal is a small to medium tree in the family Fabaceae. The genus Acacia dominates large areas in some east African countries. Acacia seyal afford "Gum Arabic" which is a heteropolysaccharide. The plant is claimed to possess therapeutic properties. In this study the heartwood of Acacia seyal were extracted with ethanol. The ethanolic extract was purified by paper chromatography and a pure flavonol was isolated. The structure of this flavonoid has been elucidated via its spectral data. Furthermore, the antioxidant and the antimicrobial activity of the isolated flavonol have been assessed. Compound I showed significant free radical scavenging properties. Compound I showed excellent activity against Pseudomonas aeruginosa and Bacillus subtilis. It also exhibited moderate activity against Escherichia coli.