This manuscript describes the synthesis of virus capsid protein-coated Au nanoparticle (VP-AuNP) without the use of the inherent self-assembly of virus proteins into virus particles. Covalent binding between Au and cysteines in the virus proteins keep the cell-surface binding sites on the external surface. Based on this method, various sizes of VP-AuNP can be created in a similar manner to native virus particles. We clarified the optimum size of the VP-AuNP for internalization into cells.