Electrochemical carboxylation of phenyl-substituted vinylic bromides in the presence of atmospheric carbon dioxide using a platinum cathode and a magnesium anode gave the corresponding alpha,beta-unsaturated carboxylic acids in 63-92% isolated yields. A precursor of ibuprofen, 2-(pisobutylphenyl)propenoic acid, was readily obtained in a 93% yield by a similar electrochemical carboxylation of 1-bromo-1-(p-isobutylphenyl)ethene. Stereochemical studies showed that thermodynamically less stable Z-isomers were preferentially produced from either E- or Z-vinylic bromides in these electrochemical carboxylations.