Carbon nanotube supported metal nanoparticles (NPs) have attracted considerable attention due to their great potential for heterogeneous catalysis. In this paper, surfactant-free and well dispersed platinum (Pt) NPs supported on multi-walled carbon nanotubes (MWCNTs) were synthesized by immobilization of negatively charged Pt precursor (PtCl42-) onto positively charged MWCNTs (NH3+-MWCNTs) by electrostatic interactions, which was reduced subsequently to Pt NPs of similar to 2 nm supported on MWCNTs by heating in 4% H-2 atmosphere. The Pt loading on MWCNTs could be controlled by the pH of the suspension of Pt precursor and MWCNTs, and the Pt-precursor concentration in the suspension. These Pt NPs supported on MWCNTs showed comparable oxygen reduction reaction (ORR) activity to a commercial Pt catalyst supported on high-surface-area carbon but with enhanced durability. (C) 2011 The ElectrochemicalSociety. [DOI: 10.1149/2.066111jes] All rights reserved.