The bis(imino)pyridyl vanadium(III) complex [VCl3-{2,6-bis[(2,6-iPr(2)C(6)H(3))N=C(Me)](2)(C5H3N)}] activated with different aluminum cocatalysts (AlEt2Cl, Al2Et3Cl3, MAO) promotes chemoselective 1,4-polymerization of butadiene with activity values higher than classical vanadium-chloride-based catalysts. The polymer structure depends on the nature of the cocatalyst employed. The MAO-activated complex was also found to be active in ethylene-butadiene copolymerization, producing copolymers with up to 45 mol-% of trans-1,4-butadiene. Crystalline polyethylene and trans-1,4-poly(butadiene) segments were detected in these copolymers by DSC and C-13 NMR spectroscopy.