The present invention provides an industrially safe, easily operable process for producing an optically active epoxy alcohol derivative useful as an intermediate for pharmaceuticals from inexpensively available materials, and also provides a novel halohydrin derivative serving as an important intermediate for the epoxy alcohol derivative. Furthermore, the present invention provides a process for producing an intermediate for a triazole antifungal agent by allowing a halohydrin to react with a triazole sulfonamide, the process including a small number of steps. A process for producing an optically active epoxy alcohol derivative includes allowing an optically active .alpha.-substituted propionate derivative to react with a haloacetic acid derivative in the presence of a base to prepare an optically active haloketone derivative, allowing the resulting haloketone derivative to react with an aryl metal compound to stereoselectively prepare a halohydrin derivative, eliminating a substituent for the hydroxy group of the halohydrin derivative, and performing epoxidation with a base. Furthermore, a process for producing an intermediate for a triazole antifungal agent includes allowing a halohydrin derivative to react with a triazole sulfonamide, the process including a small number of steps.