A thermoplastic foam is provided which contains a thermoplastic resin and a layered silicate and in which foam cells and the layered silicate are evenly and finely dispersed. A volume-expansible gas or heat decomposable blowing agent is incorporated into interlayer spaces of a layered silicate in a composite material containing 100 parts by weight of a thermoplastic resin and 0.1-50 parts by weight of the layered silicate, and the gas or blowing agent is allowed to expand in volume or thermally decompose to form foam cells 6, so that a thermoplastic foam is obtained in which the layered silicate has an average interlayer spacing of over 60 Å when determined by an X-ray diffractometry.