A new highly active coordination catalyst system, based on calixarene–neodymium complex using di- n-butyl magnesium as a cocatalyst and hexamethyl phosphoramide (HMPA) as an additive, for polymerization of styrene was developed for the first time. The catalytic activity of this new catalyst is 0.50–1.0×10 3 Kg PSt/mol Nd h with a molecular weight range of 6–12×10 4 in solution polymerization and 1.3×10 3 Kg PSt/mol Nd h with a molecular weight of 22×10 4 in bulk polymerization under the following conditions: [Nd]=2.0×10 −4 mol/l, Mg/Nd=100, HMPA/Mg=1, T=70°C, time=4 h.