A series of 2,6-bis(imino)pyridyl iron(III) complexes of the general formula [2,6-(ArN CMe) 2C 5H 3N]FeCl 3 (Ar = –C 6H 5, 3a; 2-MeC 6H 4, 3b; 2-EtC 6H 4, 3c; 2- iPrC 6H 4, 3d; cyclohexyl, 3e; 4-MeC 6H 4, 3f; 4- iPrC 6H 4, 3g; 4-FC 6H 4, 3h and 4-CF 3C 6H 4, 3i), activated by alkylaluminum, MAO or MMAO, have been investigated in 1,3-butadiene polymerization. Iron(III) complex ( 3a), with the least steric hindrance around the metal center, gives polymer up to 99% in yield in 4 h (butadiene to iron ratio = 1000), and trans-1,4 selectivity about 94.7% at room temperature in toluene, while those ( 3b– 3d) bearing alkyl substituents at the 2-position of each N-aryl ring exhibit much lower catalytic activity and tunable trans-1,4 selectivity. Introduction of an alkyl group at the 4-position ( para-position, 3f and 3g) exerts a slightly beneficial effect on the trans-1,4 selectivity, while electronegative groups at the same position ( 3h and 3i) affect negatively on the activity. The effects of temperature, types of cocatalyst and Al/Fe molar ratio on the polymerization behavior are investigated. More importantly, a mechanism for forming trans-1,4 structure is also proposed.