Abstract: A novel type of macromolecular antioxidant HACP with a P-N structure and six new functional hindered phenol branches was synthesized in a two-step procedure. An amine terminated-cyclotriphosphazene intermediate was first synthesized by using six 4-hydroxy phenyl acetamide and hexachlorocyclotriphosphazene as the raw materials, and then HACP was synthesized sucessfully through the amidation condensation reaction of this intermediate with β-(3,5-diterbutyl-4-hydroxyphenyl) propionyl chloride. The chemical structure of HACP was analyzed by FTIR and NMR spectra, and a comparative investigation on the thermal and oxidation resistance properties of modified polypropylene (PP) by HACP and Irganox 1010 were performed. The TGA results indicated that the HACP-modified PP achieved a better thermal stability by presenting a higher characteristic temperature at the weight loss of 5 wt %. The HACP and Irganox 1010-modified PP compounds well preserved their mechanical properties after 2-week aging, whereas the mechanical properties of pure PP decreased a lot. Compared to pure PP, the HACP-modified PP showed a decrease in tensile strength by 11.6 %, whereas the Irganox 1010-modified one presented a more significant decrease by 11.6 %.