Layered inorganic-organic composites, 2 : 1 type vinyl(or 3-mercaptopropyl) magnesium phyllosilicate, were synthesized at room temperature by the reaction of vinyltrimethoxysilane (or 3-mercaptopropyltrimethoxysilane) to magnesium chloride hexahydrate. These hybrid materials were studied by X-ray diffraction and infrared spectroscopy. These polymers have an inorganic part of phyllosilicate-like structure such as talc or smectite, and organic side chains linked to the inorganic framework through an -Si-C- covalent bond. The 1ayered inorganic parts were considered consistent with well ordered octahedra1 sheets and disordered --C-SiO₃ tetrahedral sheets. The tendency of magnesium ion to form octahedral sheets played major part in the formation of the layered structure.