PURPOSE: The titled composition suitable for sealing electronic parts, etc., having improved water-vapor resistance free from bad influence of impure ion, obtained by blending an epoxy resin with novolak phenolic resin, a highly water absorbing resin and a fixed amount of an inorganic filler.

CONSTITUTION: (A) An epoxy resin (e.g., bisphenol type aromatic epoxy resin, etc.,) is blended with (B) novolak phenolic resin, (C) 25W90wt% based on a resin composition of an inorganic filler (e.g., silica powder, alumina, etc.,) and (D) a highly water absorbing resin (preferably having higher water absorption then mixed substance of the components A, B and C), to give the aimed composition. An equivalent ratio of epoxy group of the component A/phenolic hydroxy group of the component B is preferably 0.1W10.