Folkloric use of root-bark extract of Alstonia boonei in the treatment and management of many disease conditions may be associated with free radical scavenging as part of its mechanisms of action. We therefore evaluated the ability of different solvent fractions of the methanol extract, crude precipitate from the extract, and isolated compound from the crude precipitate for scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. Phytochemical analysis revealed the presence of useful phytocompounds. Ethyl acetate fraction showed better antioxidant activity with IC50 of 54.25 μ g/mL while acetone and methanol fractions have 121.79 and 141.67 μ g/mL, respectively. The crude precipitate and isolated compound showed IC50 values of 364.39 and 354.94 μ g/mL, respectively. The crude precipitate, fractions, and compound 1 showed antioxidant activity against DPPH radical although lower than that of ascorbic acid.