Monodisperse Pt nanoparticles (NPs) studded in a three-dimensional (3D) graphene nanobox are successfully synthesized through a simple in-situ confined growth route for the first time. The nano-zeolite A was used as a 3D substrate for in-situ growth of tri-layered graphenes on the crystal-surfaces, meanwhile, the inner micropores of which can also be utilized for the confined growth of Pt nanoparticles. The graphene sheets are curved on the edges to form a 3D hollow box morphology, where the monodisperse Pt nanoparticles are homogeneously studded on the inner surfaces. Moreover, the Pt content can be regulated from 8 to 50 wt , and the particle size can be tuned from 2-5 nm by varying the pristine Pt-ion loading amount and CVD temperature. The Pt NP@graphene nanoboxes possess not only large pore volumes to effectively accommodate large amounts of oxygen, but also supply excellent electrical conductivity for the fast transfer of electrons ( 3.96 e-), resulting in a high efficiency (175 mA/mg Pt) and long-term stability (above 1000 cycles) for the oxygen reduction reaction.