The aluminum aryloxide was prepared via the reaction of phenolic antioxidant, 3-(3,5-di-t-butyl-4-hydroxyphenyl)-N-octadecylpropionamide, with triethyl aluminum. Propylene polymerization using supported Ziegler-Natta catalyst systems was carried out in the presence of the antioxidant or its aluminum aryloxide. Although the antioxidant gave rise to decrease in catalyst yield and change in hydrogen response, the aluminum aryloxide had no influence on the catalytic polymerization behavior, and thus the obtained polymer characteristics such as molecular weight, polydispersity, and meso pentad as a stereoregularity were comparable to that polymerized without the antioxidant and the aluminum aryloxide. Polypropylene obtained in the presence of the aluminum aryloxide was well stabilized for oxidation and its stability was over 1000 h at 100 degrees C (estimated to be over 30 years at room temperature). (c) 2005 Wiley Periodicals, Inc.