The kinetics of oxidation of phenol and a few ring-substituted phenols by heteropoly 11-tungstophosphovanadate(V), [PV V W 11 O 40 ] 4-(HPA) have been studied spectrophotometrically in aqueous acidic medium containing perchloric acid and also in acetate buffers of several pH values at 25°C. EPR and optical studies show that HPA is reduced to the one-electron reduced heteropoly blue (HPB) [PV IV W 11 O 40 ] 5-. In acetate buffers, the build up and decay of the intermediate biphenoquinone show the generation of phenoxyl radical (ArO Á ) in the rate-determining step. At constant pH, the reaction shows simple second-order kinetics with first-order dependence of rate on both [ArOH] and [HPA]. At constant [ArOH], the rate of the reaction increases with increase in pH. The plot of apparent second-order rate constant, k 2 , versus 1/[H ? ] is linear with finite intercept. This shows that both the undissociated phenol (ArOH) and the phenoxide ion (ArO -) are the reactive species. The ArO --HPA reaction is the dominant pathway in acetate buffer and it proceeds through the OH -ion triggered sequential proton transfer followed by electron transfer (PT-ET) mechanism. The rate constant for ArO --HPA reaction, calculated using Marcus theory, agrees fairly well with the experimental value. The reactivity of substituted phenoxide ions correlates with the Hammett r ? constants, and q value was found to be -4.8. In acidic medium, ArOH is the reactive species. Retardation of rate for the oxidation of C 6 H 5 OD in D 2 O indicates breaking of the O-H bond in the rate-limiting step. The results of kinetic studies show that the HPA-ArOH reaction proceeds through a concerted proton-coupled electron transfer mechanism in which water acts as proton acceptor (separated-CPET).