A method of modifying an enzyme whereby the coenzyme-dependency of an oxidoreductase is changed is developed. Using this method, a novel carbonyl reductase variant capable of using NADH as a coenzyme is provided. It is also intended to provide a process of enzymatically producing an optically active (S)-4-halo-3-hydroxybutyric acid ester by using the carbonyl reductase variant. A method of modifying an enzyme itself so as to change the coenzyme-dependency of carbonyl reductase which asymmetrically reduce a carbonyl compound to give an optically active alcohol; a carbonyl reductase having been converted in the coenzyme-dependency from NADPH to NADH which is obtained by the above method; DNA encoding this enzyme variant; a plasmid having this DNA; transformant cells transformed by this plasmid; and a process for producing an optically active alcohol by using the above enzyme variant and/or the above transformed cells.