Novel SiO₂/SiO₂ core-shell monodisperse silica spheres for high performance liquid chromatography (HPLC) packing materials are prepared by the layer-by-layer self-assembly technique. The core-shell silica spheres consist of micrometer-sized porous silica spheres as core and a thin mesoporous silica shell formed from multilayer nanometer-sized silica particles. In addition, a reversed-phase packing by bonding octadecyltrichlorosilane on SiO₂/SiO₂ particles through alkyl modified method is prepared and characterized. The results show that the carbon content of the new reversed-phase stationary phase increases approximately by 45% compared with the uncoated octadecyl-bonded SiO₂ stationary phase. Eight kinds of tested aromatic compounds are wellseparated on the packing and the peaks are symmetrical, which demonstrate that the packing acts as a truely reversed-phase chromatographic stationary phase.