The acid catalyzed decomposition of p-tert-butylcumene hydroperoxide results in acetone and p-tert-butylphenol as the main products. This paper deals with the experimental results obtained on strongly acidic activated cation exchanger resins. Analysis of the data revealed that product formation is mainly due to an addition product (2-hydroxy-isopropyl-p-tert-butylcumyl peroxide) of p-tert-butylcumene hydroperoxide and acetone which reacts faster than the hydroperoxide itself. If no acetone was added to the hydroperoxide reactant at the beginning of the reaction the step referred to becomes autocatalytic. This character prevails for a period of time but ceases at higher acetone accumulation. A simple pathway is suggested for the decomposition which is supported by the kinetic analysis carried out for the pseudo-heterogeneously reacting system.