The present invention relates to a continuous process for preparing optically pure (S)-3-hydroxy-&ggr;-butyrolactone expressed by the following Formula 1 and more particularly, to a process which enables preparing optically pure (S)-3-hydroxy-&ggr;-butyrolactone economically in large quantities, by: (a) Preparing &agr;-(1,4) linked oligosaccharide with adequate sugar distribution by reacting amylopectin which is easily available from natural product with enzyme under a specific condition; and (b) Performing oxidation, esterification and cyclization sequentially under a specific condition.