A thermosetting resin composition capable of providing a molding, such as a resin sheet, that excels in not only dielectric characteristics but also dimensional stability at high temperature and even after exposure to high temperature thermal history, exhibits little dimensional change by the thermal history, namely, exhibiting low linear expansion coefficient. There are further provided a resin sheet and resin sheet for insulated substrate produced from the thermosetting resin composition. In particular, there is provided a thermosetting resin composition comprising an epoxy resin of 100 to 2000 epoxy equivalent, an epoxy resin hardening agent consisting of a phenolated compound, and a layered silicate, and are further provided a resin sheet comprised of the thermosetting resin composition and a resin sheet for insulated substrate comprised of the resin sheet.