A new mixed layer silicate useful for industrial materials is provided.The mixed layer silicate is obtained by a specific synthesis method. The mixed layer silicate includes non-swelling 2:1 type layered silicate layers having a layer charge of 0 or non-swelling 2:1 type layered silicate layers having a layer charge of 0.6 to 1 and including potassium ions between layers and swelling 2:1 type layered silicate layers having a layer charge of 0.2 to 0.6 and including exchangeable cations between layers. The mixed layer silicate has a structure in which individual layers are laminated in a regular order in a lamination direction (regularly mixed layer structure). Furthermore, an organic-inorganic composite material is prepared through intercalation of a positive charge organic compound into the swelling 2:1 type layered silicate layers in the resulting mixed layer silicate, and the resulting organic-inorganic composite material is swollen and peeled in a polymer, so that a polymer composite material in which silicate sheet sets, each set including a few silicate sheets, are homogeneously dispersed in the polymer can be obtained.