Herein, we present the synthesis and application of a new type of graphene-based magnetic and plasmonic nanocomposite for magnetic-field-assisted drug delivery and chemo-photothermal synergistic therapy. The nanocomposites were prepared via conjugation of the PEGylated Fe₂O₃@Au core/shell nanoparticles (Fe₂O₃@Au NPs) with reduced graphene oxide (rGO). The hybrid nanostructures (rGO–Fe₂O₃@Au NPs) are superparamagnetic and show great photothermal conversion efficiency under 808 nm near-infrared (NIR) laser irradiation and high drug loading ability (1.0 mg mg⁻¹). MTT cell viability assay demonstrates that the chemotherapeutic drug, doxorubicin loaded rGO–Fe₂O₃@Au NPs (DOX–rGO–Fe₂O₃@Au NPs) have synergistic interaction between photothermal therapy (PTT) and chemotherapy. Furthermore, in vitro studies using HeLa cells show that the chemo-photothermal therapeutic efficacy of DOX–rGO–Fe₂O₃@Au NPs can be dramatically improved by the assistance of magnetic-field-guided drug delivery.