The polymerization of epsilon-caprolactone (epsilon-CL) with a combination of tert-butyllithium (t-BuLi) and bis(2,6-di-t-butylphenoxy)methylaluminum [MeAl(ODBP)(2)] in toluene at 0 degrees C proceeded in a living manner to give polymers with narrow molecular weight distributions ( MWD) within a few minutes, while the polymerization with t-BuLi alone gave a polymer with much broader MWD. The yield of the polymer did not reach 100% at the Al/Li ratio of 5, because the excess MeAl(ODBP)(2) coordinates with epsilon-CL to protect it from the attack by the propagating species. The polymerization with t-BuLi/EtAl(ODBP)(2) gave polymers in quantitative yields regardless of Al/Li ratio, and also narrower MWD even for higher molecular weight polymers.