Vinyl acetate and methyl acrylate living radical polymerization were successfully mediated by cobalt(II) Salen* complexes. Living characters of the polymerization are demonstrated by the linear increase in molecular weight with conversion, low polydispersity (1.14–1.27), and the formation of block copolymers. The equilibrium between cobalt(II) and organo-cobalt(III) species in methyl acrylate polymerization was followed by UV-vis spectroscopy and the equilibrium constant was determined to be 2.4 × 10⁷ M⁻¹.