Abstract: The thermal degradation behaviors of polypropylene (PP)/multi-walled carbon nanotubes (MWCNTs) composites were investigated by a thermogravimetric (TGA) method, and their thermal degradation mechanisms were studied by the Achars and Coats-Redferns methods. The Kissingers method was also used to obtain the related kinetic parameters and thermal life equation. The results indicated that there was a weightless stage in the TGA thermograms of the composites. Furthermore, the initial weight-loss temperature and maximum weight-loss temperature exhibited a maximum value at 1.5 wt % of MWCNTs, indicating an improvement in thermal stability of PP. The thermal degradation mechanism was ascribed to a one-dimensional diffusion reaction. The thermal life of the composites was also improved significantly due to the incorporation of MWCNTs. The composites showed an increasing trend in thermal life with an increase of MWCNTs content and achieved a maximum thermal life at the MWCNTs content of 1.5 wt %. The Kissinger methods was considered as a good solution to estimate the thermal life of materials.