A 2,3-epoxypropyl derivative or a 2-methyl-2,3-epoxypropyl derivative of a compound having carboxyl groups or amido groups is produced as a purified product having an epoxide equivalent of 1.0 to 1.1 times the theoretical epoxide equivalent of the derivative, an ionic halogen content of 10 ppm or less, transparency when molten and a stability against increase in the epoxide equivalent when stored at 150.degree. C. for 24 hours, by a process comprising steps (A) reacting 1.2 to 60 mol of an epihalohydrin or a 2-methyl-epihalohydrin with 1 mol of active hydrogen atoms of the carboxyl or amido group of the compound in the presence of a particular catalyst, thereby forming a reaction product containing a 2-hydroxy-3-halopropyl derivative or a 2-hydroxy-2-methyl-3-halopropyl derivative, (B) dehydrohalogenating the derivative by adding to the reaction product a sufficient amount of an alkali metal hydroxide thereby forming a final slurry containing the 2,3-epoxypropyl derivative of the 2-methyl-2,3-epoxypropyl derivative and the alkali metal halide, (C) washing the final slurry or a liquid product formed by removing the alkali metal halide from the final slurry thereby forming a refined liquid containing the derivative, and (D) removing by evaporation the epihalohydrin or the 2-methyl-epihalohidrin from the refined liquid, thereby forming the 2,3-epoxypropyl derivative or the 2-methyl-2,3-epoxypropyl derivative as the purified product.