PURPOSE: To obtain the titled composition having excellent storage stability and thermosetting reactivity and useful as an insulation sealing material for electrical parts, etc., by mixing a molten epoxy resin with a premix composed of a curing agent having low reactivity, zeolite and a specific cure-accelerator.

CONSTITUTION: The objective composition can be produced by mixing (A) a premix composed of (i) a curing agent having low reactivity, (ii) zeolite and (iii) a phosphine or amine-based cure accelerator having surface adhesivity to the component (ii), wherein said component (iii) is essentially unreacted with the component B. The amount of the component (ii) is preferably 0.5W50pts.wt. per 100pts.wt. of the component B.