Provided is a method for preparing an epoxy compound having an alkoxysilyl group effectively by using a mild catalyst as well as an aromatic alcohol ring-opening agent. The preparation method for an epoxy compound having an alkoxysilyl group includes: performing a ring opening step by reacting an epoxy compound having an epoxide group, which is a starting material, with an aromatic alcohol ring-opening agent in the presence of a phosphine-based catalyst and an optional solvent so as to obtain an intermediate having a partially ring-opened epoxide group; and performing an alkoxysilylation step by reacting the intermediate having a partially ring-opened epoxide with isocyanate alkoxysilane.