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 tale or smectite, and organic side chains linked to the inorganic parts were considered through an -Si-C- covalent bond. The layered inorganic parts were considered consistent with well ordered octahedral sheets and disordered --C-SiO₃tetrahedral sheets. The tendency of magnesium ion to form octahedral sheets played major part in the formation of the layered structure.