The influence of ZSM-5 zeolite and Red Mud in the pyrolysis of plastic wastes has been studied. Both catalysts have been thoroughly characterized; the zeolite shows weak and strong acid sites and great BET surface area (412.0 m(2) g(-1)), while Red Mud contains lower acidity, with also weak and strong acid sites, meso-macropores and BET surface area of 27.49 m(2) g(-1). Both catalysts have been tested in pyrolysis of a mixture of plastics which resembles municipal plastic wastes, at 440 and 500 degrees C in a 3.5 dm(3) semi-batch reactor. The results have been compared with those of the thermal process. It has been proved that ZSM-5 zeolite has a strong effect in the characteristics and distribution of pyrolysis products. It generates at both temperatures a greater proportion of gases and liquids with a higher content of aromatics than without catalyst. Red Mud needs higher temperatures than ZSM-5 zeolite to exert a catalytic effect in pyrolysis, since similar results to those obtained without catalyst are obtained at 440 degrees C. while at 500 degrees C a higher yield of gases and a greater proportion of aromatics in the liquids is obtained. (C) 2011 Elsevier B.V. All rights reserved.