It has been required to economically produce a large amount of an optically active gamma-lactone derivative (for example, pantolactone) which is useful as an intermediate in synthesizing a useful substance such as a drug. To achieve this object, it is advantageous to employ a technique of enzymatic asymmetric hydrolysis with the use of an enzyme lactonase. However, it remains troublesome to prepare the enzyme or utilize a microorganism capable of producing the enzyme. Also, it is difficult to obtain a sufficient and stable enzymatic activity in the case of using recombination techniques. In producing lactonase, which asymmetrically hydrolyzes a gamma-lactone derivative such as racemic pantolactone selectively, by a recombination technique, maturation lactonase DNA and signal peptide region DNA are both transferred into a host. Thus, a stable activity comparable to that of natural lactonase can be achieved and a transformant having a high enzyme activity and sustaining it in a stable state can be obtained. As a result, it becomes possible to efficiently and industrially advantageously perform the asymmetric synthesis of a gamma-lactone derivative.