PURPOSE: To obtain a resin composition which gives a cured article having excellent flow, cracking resistance and dielectric breakdown strength, by mixing an epoxy resin and a curing agent with an inorganic fiber surface-treated with a vinylsilane compound and an inorganic powder or particles.

CONSTITUTION: 100pts.vol. epoxy resin and curing agent are mixed with 40W200 pts.vol. total of an inorganic fiber diameter of 3W20μ and a length of 3W150μ, surface-treated with a vinylsilane compound and an inorganic powder or particle having a particle size distribution containing at least 90wt% component of a particle diameter ≤10μ and at least 50wt% component of a particle diameter ≤5μ. As the vinylsilane compound used for surface treatment, vinyltri-β- methoxyethoxysilane is desirable for obtaining a remarkable effect on fluidity. Examples of said inorganic fibers include inorganic oxide fibers (e.g., Al2O3) and inorganic non-oxide fibers (e.g., Si3N4).