Fe(II) pyridinebisimine complexes activated with trialkylaluminium or modified methylaluminoxane (MMAO) as catalysts were employed for the polymerization of butyl methacrylate (BMA). Polymer yields, catalytic activities and molecular weights as well as molecular weight distributions of BMA can be controlled over a wide range by varying the reaction parameters such as cocatalyst, Al/Fe molar ratio, monomer/catalyst molar ratio, monomer concentration and reaction temperature used in the polymerization. The catalytic activity of Fe(II) complex was 11.1 kgpolym/molFe·h and the highest yield could reach 99.1% under optimum condition.