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 .ANG. when determined by an X-ray diffractometry.