A preparative-scale asymmetric synthesis of (R)-alpha-fluorophenylacetic acid, a useful chiral derivatizing reagent, is described. Starting from ethyl alpha-bromophenylacetate, alpha-fluorophenylmalonic acid dipotassinm salt was prepared in three steps (54% yield), including nucleophilic substitution by the fluoride ion as the keystep. Both the purified form and crude preparation of arylmalonate decarboxylase in E. coli worked well on this substrate, and (R)-alpha-flurophenylacetic acid (>99% e.e.) was prepared in a quantitative yield.