Construction of multifunctional nanocomposites as theranostic platforms has received considerable biomedical attention. In this study, a triple-functional theranostic agent based on the cointegration of gold nanorods (Au NRs) and superparamagnetic iron oxide (Fe3O4) into polypyrrole was developed. Such a theranostic agent (referred to as Au/PPY@Fe3O4) not only exhibits strong magnetic property and high near-infrared (NIR) optical absorbance but also produces high contrast for magnetic resonance (MR) and X-ray computed tomography (CT) imaging. Importantly, under the irradiation of the NIR 808 nm laser at the power density of 2 W/cm(2) for 10 min, the temperature of the solution containing Au/PPY@Fe3O4 (1.4 mg/mL) increased by about 35 °C. Cell viability assay showed that these nanocomposites had low cytotoxicity. Furthermore, an in vitro photothermal treatment test demonstrates that the cancer cells can be efficiently killed by the photothermal effects of the Au/PPY@Fe3O4 nanocomposites. In summary, this study demonstrates that the highly versatile multifunctional Au/PPY@Fe3O4 nanocomposites have great potential in simultaneous multimodal imaging-guided cancer theranostic applications.