A solvent-free thermosetting resin composition which comprises an epoxy resin (a) and a product (b) of the reaction of an organosilicon compound, represented by the general formula (1) (where R is an organic group containing a functional group reactive with an epoxy resin by addition reaction; and R1 is a methyl or ethyl group), with water, the product (b) containing organosilicon compound polycondensates formed in the epoxy resin (a) and having a degree of polycondensation of 2 or higher, and which has a low viscosity at a room temperature (25 C.) and gives a cured resin having intact material properties, especially intact high-temperature mechanical properties; a process for producing the resin composition; and a product obtained by applying the composition. ##STR1##