Graphene/Au composites with a high positive charge, which is advantageous for the binding and condensation of negatively charged siRNA, are synthesized via an in situ reduction method, using PEI as a reductant and protective reagent. Owing to the sufficient amounts of amino groups, PEI-grafted graphene/Au composites can be further modified with methoxyl-PEG to acquire low cytotoxicity, novel blood compatibility, and optimal dispersibility in physiological environments. The obtained PEGylated PEI-grafted graphene/Au composites (PPGA) allow efficient loading of siRNA, forming PPGA/siRNA complexes to transport into HL-60 cells and downregulated anti-apoptosis Bcl-2 protein, indicating PPGA is a suitable platform for gene delivery. Moreover, PPGA display an enhanced photothermal response with respect to PPG under NIR laser irradiation, suggesting that PPGA can be used as an efficient photothermal agent.