Inorganic/polymer Janus microspheres were fabricated successfully in a one-step process by miniemulsion polymerization. Our method involved the in situ miniemulsion polymerization of styrene and the in situ hydrolysis condensation of tetraethoxysilane under basic conditions. By taking lull advantage of phase separation between the growing polystyrene particles and tetraethoxysilane. Janus microspheres were obtained with silica constituting one hemisphere by the hydrolysis condensation and polystyrene the other hemisphere after the polymerization of monomers. The Janus microspheres showed amphiphilicity due to the different chemical composition of each hemisphere.