High temperature treatment in inert atmosphere proved to be an effective way to improve high temperature stability of MWNTs in ambient condition. TEM analysis of heat-treated MWNTs confirmed successful removal of impurities and formation of ordered graphene layers and internal bamboo structure. TG-DTG curves indicated that decomposition range and rate of as-received MWNTs were narrow and notably higher, respectively, than heat-treated MWNTs mainly due to presence of impurities like metal nanoparticles in the former. Non-isothermal kinetic analysis revealed that the rate determining mechanism for as-received MWNTs was random nucleation and growth of active species. However, for heat-treated MWNTs, rate controlling mechanism was chemical reaction. Higher activation energies (similar to 203 kJ molt and 280 kJ mol(-1)) and reaction orders (3 and 4) of MWNTs heat-treated at 1200 degrees C and 1800 degrees C in inert, respectively, indicated delayed thermal decomposition than as-received MWNTs (E-a approximate to 178 kJ mol(-1); n =1) even in oxidative atmosphere. (C) 2010 Elsevier B.V. All rights reserved.