Different dealuminated Y -zeolite samples were prepared by the removal of aluminium atoms from H4 Y-zeolite using the conventional method with chelating agent EDTA. The DTA of different dealuminated samples was investigated. The X-ray diffraction spectra of the prepared samples were also studied. The catalytic activity of these zeolite samples was tested using the cumene cracking reaction in a microcatalytic system. The results obtained revealed that the zeolite samples are thermally stable. The degree of crystallinity was nearly the same as the original, except for samples with a degree of dealumination higher than 40%. In the cumene cracking study, the reaction