PURPOSE: To prevent diethylethanolamine which is used as a synthetic intermediate of coatings, medicines and a variety of chemicals, from being discolored, by allowing diethanolamine synthesized from diethylamine and ethylene oxide to contact with a reducing agent.

CONSTITUTION: The crude mixture resulting from the reaction between diethylamine and ethylene dioxide is distilled to remove low boiling components such as ethylamine, alcohols or the like. Then, a reducing agent such as a metal hydride such as aluminum borohydride is used to avoid the discoloration of the diethanolamine. A trace amount of oxygen dissolved in the product which cannot be removed by bubbling an inert gas oxidizes by-products such as ethers or ketones formed by the reaction to cause discoloration, and the reducing agent removes these by-products, thus discoloration is prevented.