[PROBLEMS] To provide a method by which desired optically active carboxylic acids may be prepared from a carboxylic acid having a carbon-carbon double bond through asymmetric hydrogenation with a catalyst consisting of a transition metal complex containing a water-soluble ligand and which permits easy separation of the used catalyst from the product by liquid-liquid separation alone and enables the recovery of an expensive transition metal and the reuse of the catalyst.[MEANS FOR SOLVING PROBLEMS] Phosphines represented by the general formula (1): ##STR00001## wherein X.sup.1 is oxygen or methylene; X.sup.2 is methylene, ethylene, trimethylene, 1,2-dimethylethylene, isopropylidene, or difluoromethylene; A is a Group IA alkali metal of the periodic table, hydrogen, or an ammonium ion; and a, b, c and d are each an integer of 0 or 1, with the proviso that the cases wherein the sum of a, b, c, and d is 0 are excepted.