We present the functionalization of graphitized carbons via simple diazonium reaction as a method for preparation of highly durable Pt catalyst supports for polymer electrolyte membrane fuel cells (PEMFCs). The functionalization of the graphitized carbon supports with the trifluoromethylphenyl groups via diazonium coupling reaction was shown to improve the dispersion of Pt nanoparticles and to reduce the Pt sintering phenomena, resulting in high stability and activity of the Pt/functionalized carbon. This approach also holds a potential for enhancing the dispersion of Pt nanoparticles on the surfaces of graphitized carbons without any deterioration of their intrinsic properties. Electrochemical analysis demonstrates that the Pt/functionalized carbon show improved electrochemical durability than the Pt/graphitized carbon and commercial Pt/C catalyst. The functionalized surfaces of the graphitized carbons not only increases the resistance against carbon corrosion but also offers better attachment of Pt nanoparticles to the carbon surfaces, resulting in the improved durability of the Pt/functionalized carbon. This study shows that this simple functionalization of graphitized carbons by the in situ grafting of functional groups onto their surfaces is an effective way to fabricate highly durable catalysts for PEMFCs, thereby providing a design guide of the functionalized carbon supports catalysts with a great potential as PEMFC catalysts.