The polypropylene-grafted multiwalled carbon nanotubes (PP-MWCNTs) were produced from the reaction of PP containing the hydroxyl groups and MWCNTs having 2-bromoisobutyryl groups. The PP-MWCNTs had a significantly rougher surface than the original MWCNTs. PP-MWCNTs had PP layers of thickness 10-15 nm on the outer walls of the MWCNTs. PP/PP-MWCNT composites and PP/MWCNT composites were prepared by solution mixing in o-xylene. Unlike PP/MWCNT composites, PP-MWCNTs were homogeneously dispersed in the PP matrix. As a consequence, the thermal stability and conductivity of PP/PP-MWCNT composites were dramatically improved even if only 1 wt % of PP-MWNTs was added to the PP matrix. The good miscibility of PP and PP-MWCNTs plays a critical role in the formation of the homogeneous composites and leads the high thermal stability and conductivity. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012