An alternating copolymer of methyl acrylate with carbon monoxide has been synthesized for the first time via coordination polymerization using palladium complexes of phosphine-sulfonic acid as catalyst. The highly controlled head-to-tail structure of the copolymer was confirmed by NMR spectra. Susequent insertion of carbon monoxide and methyl acrylate to methylpalladium species provided gamma-ketoalkylpalladium 2. The present system apparently conquered the difficulty in coordination-insertion of CO to 2.