PURPOSE: To obtain the subject compound useful as a synthetic raw material for ferroelectric liquid crystal, etc., under mild condition on an industrial scale at a low cost by using a specific disubstituted malonic acid as a substrate and culturing a microbial strain belonging to the genus Alcaligenes and capable of assimilating phenylmalonic acid.

CONSTITUTION: A microbial strain belonging to the genus Alcaligenes and capable of assimilating phenylmalonic acid [e.g. Alcaligenes bronchisepticus KU1201 (FERM P-11670)] is inoculated on a sterilized inorganic salt medium incorporated with phenylmalonic acid. After culturing the strain at 30°C for 4 days, a disubstituted malonic acid expressed by formula I [Ar is (substituted) aromatic group] (e.g. α-fluoro-α-phenylmalonic acid monohydrate) is added to the system and the strain is cultured at 30°C for 5 days under shaking. The culture product is adjusted to pH2 with 2N hydrochloric acid and extracted with ethyl ether. The extracted liquid is dried, the solvent is distilled off and the residue is purified to obtain the objective optically active fluorine-containing α-arylalkanoic acid compound of formula II under mild condition.