A resin composition, substrate material, sheet, laminated board, resin-bearing copper foil, copper-clad laminate, TAB tape, printed board, prepreg and adhesive sheet are provided which exhibit improved mechanical properties, dimensional stability, heat resistance and flame retardance, particularly high-temperature physical properties. The resin composition containing 100 parts by weight of a thermosetting resin and 0.1-65 parts by weight of a layered silicate inorganic compound, the resin composition having a mean linear expansion coefficient (.alpha.2) of up to 17.times.10.sup.-3 [.degree. C..sup.-1 ] over the temperature range from a temperature 10.degree. C. higher than a glass transition temperature of the resin composition to a temperature 50.degree. C. higher than the glass transition temperature of the resin composition.