We developed a versatile and facile method for synthesizing gold core-based nanoreactor with yolk/shell structure using branched polyethyleneimine (bPEI) as the carbon source for the first time. Colloidal gold particles were first synthesized and covered with a silica layer to form AuNPs@SiO₂ spheres, and then, the spheres were coated by a layer of bPEI. The hydrothermal carbonization of as-prepared AuNPs@SiO₂@bPEI gave AuNPs@SiO₂@bPEI-derived carbon nanoparticles (CNPs). The transformation from core/shell to yolk/shell structure was achieved through selective etching of the silica layer. The yolk/shell AuNPs@bPEI-derived CNPs was successfully employed in the catalytic reduction of 4-nitrophenol as a model reaction.