A new highly active rare earth coordination catalyst composed of rare earth phosphonate, di-n-butylmagnesium (MgBu), and hexamethyl phosphoramide (HMPA) for the polymerization of styrene has been developed for the first time. High molecular weight polystyrene (<(M)over bar (v)> = 50-70 x 10(4)) in 100% conversion could be prepared at following conditions : [Nd] = 6-8 x 10(-4) mol/L, [St] = 3.0 mol/L, Mg/Nd = 11, and HMPA/Mg = 1-1.5 (molar ratio). The catalytic activity of this new catalyst is 3530 g PSt/g Nd. Kinetics study shows that the polymerization rate is of first order with respect to both monomer concentration and catalyst concentration, and activation energy of the polymerization is 40.1 kJ/mol.