CoFe₂O₄@MnFe₂O₄/polypyrrole nanocomposites, in which CoFe₂O₄@MnFe₂O₄ core/shell nanoparticles (NPs) were well-distributed in/on polypyrrole (PPy) nanoparticles, have been prepared by the polymerization of pyrrole by Fe³⁺ in the presence of polyvinyl alcohol (PVA) and CoFe₂O₄@MnFe₂O₄ NPs. In CoFe₂O₄@MnFe₂O₄/polypyrrole nanocomposites, the PPy with strong near-infrared absorption can convert 808 nm laser irradiation to heat with a photothermal conversion efficiency of ∼38%, and the CoFe₂O₄@MnFe₂O₄ NPs can convert the electromagnetic energy to heat simultaneously in an alternating magnetic field (200 kHz, 60.6 kA m⁻¹) with a specific loss power of 930 W g⁻¹. In vitro experiments showed that the cell viability of 4T1 cells incubated with 200 μg mL⁻¹ of nanocomposites was ∼58% when irradiated by an 808 nm laser (0.2 W cm⁻²) for 10 min, and ∼68% in an alternating magnetic field (200 kHz, 60.6 kA m⁻¹) for 0.5 h. A combination of 808 nm laser irradiation and alternating magnetic field can ablate nearly all the cells, which suggests the synergistic effect of photothermal and magnetothermal combined therapy.