To provide a composition for obtaining an epoxy resin having favorable properties by curing an epoxidized natural oil in the presence of a silicon compound, to provide a method for obtaining the epoxy resin from the composition, and to provide the epoxy resin by the method.

The composition comprises the epoxidized natural oil or a derivative thereof and the cage-structured silicon compound such as of the formula(1)(wherein, at least one X is a group having an epoxy group, the others being each H, an alkyl, aryl or arylalkyl group). The epoxy resin having excellent properties including hardness can be obtained by using the composition. This epoxy resin gives high-quality coating films and the like.