Mesoporous hollow carbon spheres with Pt nanoparticles (NPs) loaded on their inner walls (Pt@HC-meso) have been designed and prepared through a dual-templating method. The core–shell structured Pt/SiO2@micelle-polydopamine (PDA) precursor is obtained by first depositing Pt NPs on silica spheres and then coating them with the carbon precursor of PDA and diblock copolymer micelles as soft templates. The subsequent carbonization and KOH etching convert the micelle-PDA shells into mesoporous carbon and remove the silica cores, respectively. Thus, the Pt NPs are subjected to calcination and left on the inner walls. The fabricated Pt@HC-meso achieved high electrocatalytic performance and outstanding stability in catalyzing methanol oxidation. We infer that the mesoporous carbon shells not only provide accessible diffusion pathways for the reactants, but also protect the inner Pt NPs from collision with Pt NPs in other hollow carbon spheres. Each hollow carbon sphere with Pt NPs inside can be regarded as an independent nanoreactor. Moreover, observations of the morphology have proved that the calcined Pt NPs avoid a second aggregation during the electrocatalytic process and maintain long-term stability.