Highly active half-metallocene amidinate yttrium catalysts for chemoselective and living polymerization of allyl methacrylate are reported. The living characteristics of allyl methacrylate polymerization have been proved by three sets of experiments. The generated polymers exhibit good solubility in DMF, well-controlled molecular weights, and narrow molecular weight distributions (D < 1.10). The kinetic studies revealed that the catalyst systems follow a living monometallic coordination addition polymerization mechanism. The present study is first example for rare earth metal-catalyzed living coordination addition polymerization of polar divinyl monomers.