An easy and versatile method for the covalent functionalization of graphene oxide (GO) is reported. The functionalized GO is synthesized by a polyphosphoric acid-catalyzed cyclization reaction of the carboxylic groups on GO with the hydroxyl and amino groups on o-aminophenol and o-phenylenediamine, resulting in it being well dispersed in many organic solvents. The results may provide a way to extend the use of GO as a functional material in electronic devices and high performance structural materials.