Rattle-like polymer capsules with multicores in one shell are facilely fabricated by oil-in-water Pickering emulsion polymerization for the first time. The oil phase contains hydrophobic silica nanoparticles dispersed in polymerizable monomer, styrene, and unpolymerizable solvent, hexadecane. The multicore rattle-like capsules are facilely produced after the polymerization of monomers in the oil droplets. The key point of this one-pot method lies in the nucleation of hydrophobic silica and the phase separation between the resulting polystyrene and hexadecane. The influences of the contents of silica, hexadecane, cross-linker, and stabilizer on the structure and morphology of rattle-like capsules are systematically investigated. Moreover, functionalization of the rattle-like capsules can be developed easily by varying hydrophobic nucleation nanoparticles in the oil phase. This work opens up a new route to fabricate multilevel capsules or spheres.