A novel glycidyl sulfonamide compound having a (poly)siloxane main chain of its molecule is used alone or in admixture with an epoxy resin to give a cured material being excellent in flexibility, elongation and impact strength without deteriorating thermal resistance, chemical resistance and water absorption thereof. An epoxy resin composition or a resin composition for an epoxy paint containing a glycidyl sulfonamide compound, the epoxy resin and a curling agent for epoxy resin provides a cured material or a coating film having the above-mentioned excellent properties. A process for preparing a glycidyl sulfonamide compound characterized in that subjecting an amine modified silicone having a (poly)siloxane main chain of its molecule to condensation reaction with a sulfonyl chloride to give a sulfonamide compound, which is subjected to an addition reaction with an epihalohydrin to give the glycidyl sulfonamide compound.