Polystyrene(PSt)-based copolymer/montmorillonite(MMT) nanocomposites were prepared by an in situ vapor-phase-assisted surface polymerization (VASP) as a solventless method using an organically modified MMT and a free radical initiator. Simultaneous and consecutive VASP of styrene (St) and methyl methacrylate (MMA) on the premodified MMT induced the accumulation of poly(MMA-ran-St) and poly(MMA-block-St) on the MMT surface, resulting in effective intercalation and exfoliation of silicate layers. The homogeneously dispersed silicate platelets in the polymer matrices were confirmed by X-ray diffraction and transmission electron microscope analyses. An important contributor to this phenomenon must be the particular interaction between a small amount of MMA units and silicate surfaces. This approach allows the nanocomposites with accompanying intercalation and exfoliation of silicate layers to be applied to a wide range of vaporizable monomers which in the absence of this technique would be otherwise difficult to individually prepare.