To provide a resin composition capable of satisfying both of a good thermoconductivity and a low dielectric tangent (tan ).

This resin composition containing ceramics particles in its base material resin and having 0.82 tan ratio and also 1.5 thermoconductivity ratio of the ceramics particles to the base material resin is provided with that the ceramics particles satisfy the following requirements (I) to (III): (I) In the ceramics composition, the total amount of Al2O3 or MgO and SiO2 is 80 wt.%. (II) The weight ratio of the Al2O3 or MgO to SiO2 [(Al2O3 or MgO)/SiO2] is 0.1 to 15. (III) The sphericity is 0.9.