The present invention is to provide a process for simply producing an optically active 3-hydroxypropionic ester derivative useful as a medicament intermediate from an inexpensive material. More specifically, the present invention is directed to a process for producing an optically active 3-hydroxypropionic ester derivative comprising reacting an acetic ester derivative available at low cost with a base and a formic ester, thereby converting the acetic ester derivative into a 2-formylacetic ester derivative, and thereafter, stereospecifically reducing the formyl group of the derivative by use of an enzymatic source capable of stereoselectively reducing the formyl group of the derivative.