The gas phase polymerization of 1,3-butadiene (Bd), with supported catalyst Nd(naph)(3)/Al2Et3Cl3/ Al(i-Bu)(3) or/and Al(i-Bu)(2)H, was investigated. The polymerization of Bd with neodymium-based catalysts yielded cis-1,4 (97.2-98.9%) polybutadiene with controllable molecular weight (MW varying from 40 to 80 x 10(4) g mol(-1)). The effects of reaction temperature, reaction time, Nd(naph)(3)/ Al(i-Bu)(3) molar ratio, and cocatalyst component on the catalytic activity and molecular weight of polymers were examined. It was found that there are two kinds of active sites in the catalyst system, which mainly influenced the MW and molecular weight distribution of polybutadiene. (C) 2004 Wiley Periodicals, Inc.