The acid catalysed hydrolysis of dodecyl sulphate and,dodecyl ether sulphate surfactants is catalysed by their self-micellisation. The reaction was investigated throughout the isotrooic micellar phase (up to O.6M surfactant) at 70°C. The effects of temperature, counterion,.electrolytes, acid concentration and surfactant concentration on the rate of hydrolysis were studied and analysed in terms of a pseudo-phase/ion-exchange model.