PURPOSE: To efficiently obtain the subject compound for nonionic surfactant, etc., by reacting 1,2-isopropylidenediglycerin with fatty acids in the presence of a lipase while removing water, a lower alcohol, etc., to product a diester and then hydrolyzing the diester.

CONSTITUTION: 1mol of 1,2-Isopropylidene diglycerin is reacted with ≥1.5mol of a fatty acid (e.g. oleic acid) expressed by the formula R-COOR1 (R is a 3-21C alkyl which may have 1-2 hydroxyl groups; R1 is H or 1-6C alkyl) or its lower alkyl ester in the presence of a lipase while removing the resultant water or a lower alcohol out of the reaction system to produce a diester compound expressed by formula I. This compound is hydrolyzed in the presence of an acid (e.g. cone. hydrochloric acid) to provide the objective diglycerin-1,2-diester useful as a nonionic surfactant utilized in a wide range of fields of foods, cosmetics, medicines, etc., in high yield and high purity.