To provide a method for preparing an epoxy compound from an unsaturated compound selectively with a high yield by utilizing sunlight.

The method for preparing the epoxy compound is characterized by the following: an unsaturated compound having a carbon-carbon double bond is epoxidized; the unsaturated compound is treated with an oxidant under light irradiation in the presence of a phase transfer catalyst and an optical semiconductor catalyst; and the corresponding epoxy compound is prepared by treating the unsaturated compound having the carbon-carbon double bond with the oxidant under light irradiation in the presence of the phase transfer catalyst and the optical semiconductor catalyst.