Poly(epsilon-caprolactone)s (PCLs) with various end-capping groups were prepared upon the novel one-pot reduction-initiation strategy. The reduction-involved ring-opening polymerization developed by Guillaume et al. has been firstly extended to aldehydes and ketones. The carbonyl compound was reduced by lanthanide borohydride (Nd or Y) to intermediate, which in situ triggered the ring-opening polymerization of epsilon-caprolactone. This one-pot strategy affords an efficient access to prepare the end-capped polymers from aldehydes or ketones. The reduction-initiation process and polymers were characterized by IR, NMR and SEC, and the possible mechanism was proposed. (c) 2007 Elsevier Ltd. All rights reserved.