Disclosed is a functionalized graphene containing two or more amines having excellent electrical, thermal and mechanical properties by allowing good interfacial bonding force and uniform dispersion with a thermoplastic polymer, and a method for preparing the functional graphene. The functionalized graphene comprises a carbon material selected from the group consisting of graphene, reduced graphene, graphene oxide, and mixture thereof; and a monovalent amine group and a bivalent or higher amine group which are bonded to the carbon material.