A stereochemical study on electrochemical carboxylation of ethoxycarbonyl- or phenyl-substituted vinyl triflates was carried out. Vinyl triflates in DMF with a platinum cathode and a magnesium anode underwent electrochemical carboxylation with retention of their geometries to give the corresponding alpha,beta -unsaturated carboxylic acids in moderate to good yields. The stereochemical outcome of these electrochemical carboxylations is discussed by comparison with predominant formation of a (Z)-isomer from either (E)- or (Z)-vinyl bromides.