A method for preparing .alpha., .beta.-unsaturated carboxylic acids of the formulaR.sub.1 (R.sub.2)C.dbd.C(R.sub.3)CO.sub.2 Hwhere R.sub.1 to R.sub.3 can be hydrogen, fluorine, alkyl, or alkyl containing fluorine, but at least one of R.sub.1 to R.sub.3 is fluorine or alkyl containing fluorine. The method involves reacting an alkenyl halide containing fluorine having the general formulaR.sub.1 (R.sub.2)C.dbd.C(R.sub.3)Xwhere R.sub.1 to R.sub.3 are the same as above, and X is chlorine, bromine, or iodine with carbon dioxide in an aprotic polar organic solvent and in the presence of activated zinc. The activated zinc is activated by pretreatment with a mineral acid or acetic acid. At least one cation is present during the reaction which is an alkali metal ion, alkaline earth metal ion or ammonium ion. The cation is present in an amount of 0.01 to 50 gram atoms per one mol of alkenyl halide containig fluorine. The resulting product is hydrolyzed.