In this study, we integrated chemotherapy and photothermal therapy in a magnetically targeted doxorubicin-loaded FeO@SiO nanodrug system. Size-controllable magnetic FeO@SiO core-shell nanoparticles were synthesized via a solvothermal method and a modified Stǒber method. A molecular anticancer drug, namely, doxorubicin, was loaded onto FeO@SiO nanocomposites to form a magnetically targeted drug delivery system. This drug delivery system exhibits pH-sensitive effects on drug loading and release. The drug loading rate in a neutral environment is higher than that in an acidic environment; the opposite property is observed for the release rate. In addition, the magnetic FeO@SiO nanocomposites exhibit a satisfactory photothermal effect under NIR (808 nm) irradiation. The temperature can increase to 55 °C after only 10 min of irradiation, which effectively induces apoptosis of cancer cells in vitro. The cytotoxicity and cellular uptake of FeO@SiO@DOX nanodrugs were evaluated in A549 lung cancer cells. After treatment with FeO@SiO@DOX that contains only 10 μg/mL of DOX, 82.8% of A549 lung cancer cells can be killed. Furthermore, 81.3% of A549 lung cancer cells are killed after incubation with FeO@SiO@DOX that contains only 0.5 μg/mL of DOX and 15 min of NIR irradiation, thereby suggesting an excellent synergistic chemo-photothermal effect in tumour therapy. Our results suggest a new approach for the synthesis of a multifunctional, highly targeted, size-controlled nanodrug for tumour synergistic therapy.