A novel aluminum alkoxide, which has demonstrated efficient catalytic activities in both "living" and "immortal" ROP of lactones, is prepared and characterized. The "living" character of the aluminum complex shown in the polymerization process enabled us to synthesize the P-epsilon-CL-b-P-delta-VL block polymer in a controlled manner. The structural determination and catalytic studies suggest that during the ROP of lactones, a lactone molecule coordinates to an aluminum center forming a pentacoordinated intermediate, followed by the attack of a benzylalkoxy group on lactone initiating the polymerization.