(S)‐4‐Chloro‐3‐hydroxybutyronitrile [(S)‐CHBN] was used as a chiral building block for the preparation of atorvastatin. In this study, (R,S)‐epichlorohydrin [(R,S)‐ECH] and 1,3‐dichloro‐2‐propanol (1,3‐DCP) were investigated to prepare (S)‐CHBN by using the halohydrin dehalogenase HheC from Agrobacterium radiobacter AD1. Preparing (S)‐CHBN from (R,S)‐ECH gave a modest enantiomeric excess (ee), whereas by using 1,3‐DCP as the substrate, (S)‐CHBN was obtained with 97.3 % ee after pH optimization. However, a low ee value and low yield of (S)‐CHBN were obtained if the substrate concentration was increased to 10 g L−1. To obtain a higher ee value and yield, 16 mutants were constructed and screened. The variant W249F with improvements in activity and enantioselectivity was identified and applied at a 1,3‐DCP loading of 10 g L−1, which gave (S)‐CHBN in 86 % yield with 97.5 % ee in 1 h. This is the first report of a one‐step biocatalytic process for the preparation of (S)‐CHBN from prochiral 1,3‐DCP.