Kinetics and mechanism of scavenging of reducing free radicals by plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) are studied using pulse radiolysis technique. It scavenged superoxide radical, hydroxyethyl radical and hydrated electron with bimolecular rate constants of 8.9X10⁷, 2.3X10⁹ and 1.6X10¹⁰M^-1s^-1, respectively in aqueous-alcohol medium. Plumbagin also scavenged linoleic acid peroxyl radical and tyrosyl radical with bimolecular rate constants of 1.0X10⁸ and 7.0X10⁶M^-1s^-1, respectively. Further, redox properties of plumbagin and its transients are studied using standard redox couples and cyclic voltammetry.