Nanoparticle based image-guided therapy is an emerging technology for cancer in recent years. Here, we report simultaneous photoacoustic (PA)- and magnetic resonance (MR)-guided photothermal ablation (PTA) therapy using multifunctional superparamagnetic iron oxide-containing gold nanoshells (SPIO@AuNS). Based on the intrinsic high near-infrared optical absorbance and strong magnetic property of SPIO@AuNS, we carried out in vivo dual-modality PA-MR imaging of mouse tumors. PA- and MR-guided imaging can monitor therapeutic effect after photothermal therapy mediated by our multifunctional nanomaterial. In addition, using our pulsed laser PA technique, we also observe a clearer structure of the tumor vasculature after intravenously administration SPIO@AuNS. The novel dual PA-MRI image-guided PTA therapy provides a promising new platform for cancer diagnosis and treatment simultaneously.