Li2MnSiO4@C porous nanoboxes have been synthesized via a wet-chemistry associated solid-state reaction method. The uniqueness of this material is the hollow nanostructure with a well-crystalline porous shell composed of phase-pure Li2MnSiO4 nanocrystals, which has not been reported previously. As evidenced by powder X-ray diffraction patterns and transmission electron microscopy images, the high phase purity and porous nanobox architecture were achieved via monodispersed MnCO3@SiO2 core–shell nanocubes with controlled shell thickness. Nanocomposite of Li2MnSiO4@C and reduced graphene oxide nanosheets demonstrated excellent performance as high-capacity cathode materials for Li-ion batteries.