Hepatic cancer is a serious disease with high morbidity and mortality. Theranostic agents with effective diagnostic and therapeutic capability are highly needed for the treatment of hepatic cancer. Herein, we aimed to develop a novel mesoporous polydopamine (MPDA)-based theranostic agent for T1/T2 dual magnetic resonance imaging (MRI)-guided cancer chemo-photothermal therapy. Superparamagnetic iron oxide (SPIO)-loaded MPDA NPs (MPDA@SPIO) was firstly prepared, followed by modifying with a targeted molecule of sialic acid (SA) and chelating with Fe (SA-MPDA@SPIO/Fe NPs). After that, doxorubicin (DOX)-loaded SA-MPDA@SPIO/Fe NPs (SA-MPDA@SPIO/DOX/Fe) was prepared for tumor theranostics. The prepared SAPEG-MPDA@SPIO/Fe NPs were water-dispersible and biocompatible as evidenced by MTT assay. photothermal and relaxivity property suggested that the novel theranostic agent possessed excellent photothermal conversion capability and photostability, with relaxivity of being r = 4.29 mMs and r = 105.53 mMs, respectively. SAPEG-MPDA@SPIO/Fe NPs could effectively encapsulate the DOX, showing dual pH- and thermal-triggered drug release behavior. and studies revealed that SA-MPDA@SPIO/DOX/Fe NPs could effectively target to the hepatic tumor tissue, which was possibly due to the specific interaction between SA and the overexpressed E-selectin. This behavior also endowed SA-MPDA@SPIO/DOX/Fe NPs with a more precise T1-T2 dual mode contrast imaging effect than the one without SA modification. In addition, SAPEG-MPDA@SPIO/DOX/Fe NPs displayed a superior therapeutic effect, which was due to its active targeting ability and combined effects of chemotherapy and photothermal therapy. These results demonstrated that SAPEG-MPDA@SPIO/DOX/Fe NPs is an effective targeted nanoplatform for tumor theranostics, having potential value in the effective treatment of hepatic cancer.