The decomposition of cumene hydroperoxide (CHP) was carried out in a batch reactor over supported solid acid catalysts, acid-activated montmorillonite K10 (Mont. K10) and metal-ion-exchanged (Mont. K10), at 30-60 degreesC. The products were phenol and acetone. Supported dodecatungstophosphoric acid (DTPA) showed 100% conversion within 5 min at 30 degreesC; the results obtained over acid-activated (Mont. K10) were also comparable. The type of acidity and the strength were determined. The correlation of catalytic activity with acidity revealed that both Lewis and Bronsted acid sites promote the decomposition. The reaction was first-order with respect to CHP. The results indicate that heterogeneous catalysts may be used instead of sulfuric acid for selective decomposition of CHP into phenol and acetone with 100% conversion.