Nanocomposite structures depending on the degree of surface modification of montmorillonite (MMT) were studied. To change the degree of surface modification, MMT was treated with a controlled amount of stearylamine. The structures of MMTs and nanocomposites were investigated by X-ray diffraction. To confirm the extent of surface coverage of the stearylamine as a organophilic modifier, TGA and elemental analysis experiments were performed. Different structures (intercalated or exfoliated) of a polymer/clay nanocomposite were obtained according to the interfacial characteristics between the polymer chains and the clay by controlling the degree of surface coverage.