To provide a method for industrially and efficiently producing a triglycerol monoester having antimicrobial activity and also performances including emulsifying ability, foamability and detergency.

This method for producing a triglycerol monoester of the general formula (2) comprises conducting a deketalization or deacetalization of the corresponding compound of the general formula (1) in the presence of an acid catalyst by contacting the compound of the general formula (1) with steam (in the formulas (1) and (2), R1 and R2 are each H or a hydrocarbon group; when they are each a hydrocarbon group, they may be bound to each other to form a ring; and R3 is a hydrocarbon group).