This invention provides a process for producing an epoxytriazole derivative represented by formula (2): ##STR00001## (wherein R and Ar are defined below), which comprises a step including a reaction of an epoxy derivative represented by formula (1'): ##STR00002## (wherein R represents a hydrogen atom or C1-12 alkyl group and Ar represents an aromatic group optionally substituted by a halogen atom(s) or trifluoromethyl group(s), and X' represents a hydroxy group or leaving group), with 1,2,4-triazole in the presence of a base and water.