The catalytic decomposition processes of low- and high-density polyethylene (LDPE and HDPE) have been studied using HUSY zeolite as catalyst in a: batch reactor under dynamic conditions. The evolution of the gaseous and condensed products evolved with respect to the temperature has been analyzed and compared to that obtained under similar conditions in the thermal pyrolysis of LDPE and HDPE. The behavior of the gases generated from both polyethylenes was similar, olefins being the more abundant species. Great changes were observed in the composition of the gases evolved at different temperatures. Isoparaffins and olefins showed two maxima at low and high temperatures, whereas the remaining compounds generated presented only one maximum at high temperatures. Analysis of condensed products revealed some differences between the two polyethylenes at the end of the process. Two maxima, one at low and another at high temperatures, appeared in the catalytic pyrolysis of HDPE, where isoparaffins and aromatics were the most abundant condensed products obtained at each maximum. However in the case of LDPE, n-paraffins were the main products at the very end of the process. These different outcomes could be related to the progressive deactivation of the zeolite.