Pt/CeO2 hybrid nanostructures consisting of sub-3 nm Pt nanocrystals supported on octahedral CeO2 nanocrystals can be synthesized by in situ reduction of a Pt precursor in the presence of CeO2 octahedra. Pt/CeO2 hybrid nanostructures exhibit higher resistance to poisoning by the reaction product during the catalytic reduction of p-nitrophenol into p-aminophenol by NaBH4 as compared to the unsupported Pt nanocrystals.