Me2Si(CpSiMe3)(2)NdCl activated by n-BuMgCl at low molar ratio (1 : 1.2) was successfully used to polymerize methyl methacrylate (MMA) for the first time. Grignard reagent indicated better co-catalytic properties than alkyl aluminum. Effects of the catalyst concentration, polymerization time, temperature, and solvents were studied in bulk and solution polymerization respectively. The results showed that this catalyst system was very active for MMA polymerization in toluene at 40 degreesC, producing PMMA with high molecular weight (53.5 x 10(4)) and high conversion (100%).