The petrol extract of the root bark of Milletia thonningii afforded β-amyrin and O,O-dimethylalpinumisoflavone, together with the new compounds 5-O-methyl-4 -O-(3-methyl-2-butenyl)alpinumisoflavone and thonninginisoflavone. The structures were determined by spectroscopic methods and partly by chemical interconversions. The absolute configuration of thonninginisoflavone was established by chiroptical studies. The crude extract and some of the pure compounds were active in the brine shrimp lethality bioassay.