The effect of sodium dodecyl sulphate (SDS) on the rate of oxidation of benzaldehyde (PhCHO) by permanganate (MnO-4) in perchloric acid medium has been studied. A mechanism involving the formation of an association complex between PhCHO and SDS micelle followed by its reaction with permanganate to give products has been suggested. The thermodynamic parameters of the reactive process have been evaluated.