Provided are an alkoxysilylated epoxy compound, a composite of which exhibits good heat resistance properties, low CTE and increased glass transition temperature, and a cured product thereof exhibits good flame retardancy without requiring separate coupling agent, a method for preparing the same and a composition and a cured product including the same. An alkoxysilylated epoxy compound including an epoxy group and at least one alkoxysilyl group of an S1 substituent selected from Formulae S11 to S15 or an S2 substituent selected from Formulae S21 to S25; a method for preparing the same by epoxy ring-opening reaction of starting material and alkoxysilylation, an epoxy composition including the epoxy compound, and a cured product and a use of the composition, are provided. Since chemical bonds may be formed between alkoxysilyl group and filler and between alkoxysilyl groups, chemical bonding efficiency of the composite may be improved.