Bivalent rare earth chlorides——NdCl2-nTHF and SmCl2——have been synthesizedthrough the reduction of corresponding trivalent chlorides with Lithium/Naphthaline in THF. Their catalytic activity for butadiene polymerization was studied. The system composed of NdCl2.nTHF and Et3Al showed a moderate catalystic activity while that composed of SmCl2 and Et3Al was inactive. The difference in activity between NdCl2. nTHF and SmCl2 was discussed.