Hepatocellular carcinoma (HCC) is a high incidence of disease and the high recurrence rate is a major limitation for HCC treatment. To resolve such a challenge, multimodal imaging-guided photothermal therapy (PTT) provides a promising candidate for HCC treatment. Herein, we use a facile method to develop a novel self-assembled theranostic nanoparticle (NP) based on manganese irons (Mn2+) and indocyanine green (ICG) under the protection of poly(vinylpyrrolidone) (PVP). The fabricated NPs possess the properties of strong NIR optical absorbance, high photothermal conversion efficiency and multimodal imaging. Through intravenous injection, these NPs could highly accumulate in HepG2 tumor via the enhanced permeability and retention effect, as revealed by fluorescence/photoacoustic/magnetic resonance imaging, leading to an obviously improved in vivo therapeutic outcome. This study demonstrates that our self-assembled NPs could be a potential platform for multimodal imaging-guided PTT of HCC in future clinical therapy.