This review describes a precision polymerization of 1, 3-butadiene(Bd) with metallosalen/MAO catalysts [metal=Co, Ni, Fe, V, Ti; salen=N, N′-bis (salicylidene) ethylenediamine]. 1, 4-cis selectivity and molecular weight control of the polymer of Bd with various metallosalen/MAO catalysts was investigated. Among metallosalen/MAO catalysts examined, the alkyl substituted in the aromatic ring of the (salen) Co (II) gave high molecular weight polymer with high 1, 4-cis content. In the polymerization of Bd, both polymer yields and 1, 4-cis contents increased by introducing bulky groups at suitable positions of (salen) Co (II) complexes. Simultaneous control of 1, 4-cis selectivity and molecular weight of polymer was achieved with the (salen) Co (II)/MAO catalyst which possessed tert-butyl groups at suitable positions in the aromatic rings and ethylene diamine groups substituted with phenyl group. The copolymerization of styrene and Bd with (salen) Ni (II)/MAO catalyst was also investigated.