(2R)-2-[4-(4-Cyano-2-fluorophenoxy)phenoxy]butylpropanoate (cyhalofop-butyl, CyB) was synthesized by a chemoenzymatic route involving enantioselective transesterification with Candida antarctica lipase B (Novozym 435). The optimum organic solvent, acyl donor, a (w) , reaction temperature and shaking rate for the transesterification were acetonitrile, n-butanol, 0.11, 45A degrees C and 200 rpm, respectively. Under the optimum conditions, the maximum substrate conversion and the enantiomeric purity of the product were 96.9 and > 99%, respectively. The total yield and enantiomeric purity of CyB by this chemoenzymatic synthesis were 60.4 and > 99%, respectively; 15.3 and 21% higher than that of the traditional way (45 and 78%).