Polygonum flaccidum Meissn. is an annual herb, native to Bangladesh, and well known for its analgesic, anti-inflammatory, diuretic, purgative and insecticidal properties, and also for its use against snake-bites. The analgesic and the diuretic properties of alpha-santalone (1), isolated from the aerial parts of Polygonum flaccidum, were assessed by the acetic-acid-induced writhing method and the Lipschitz test, respectively. Complete (1)H and (13)C NMR data of 1 are also presented.