In this contribution, we explored the catalytic ring-opening polymerization (ROP) of (macro)lactones using salen-aluminum complexes bearing cyclic beta-ketoiminato ligand. The effects of bridge moiety and ring size in the benzocyclane skeleton on the catalytic activity of these complexes were thoroughly investigated. Complex 5 with 2,2-dimethylpropylene bridge and five-membered cyclane ring can efficiently catalyze the ROP of omega-pentadecalactone (omega-PDL), showing higher catalytic activity (turnover frequency [TOF] up to 309.2 h(-1)) than the typical Al-salen analogs bearing salicylaldiminato ligand (TOF = 227.2 h(-1)). Thus, polyethylene-like polyester with high-molecular weight (up to 164.5 kg/mol) could be easily prepared under optimal conditions. In addition, complex 5 can also catalyze the ROP of lactide (LA) and epsilon-caprolactone (epsilon-CL) with extremely high activity (TOF is high up to 147.6 h(-1) and 4752 h(-1), respectively). Here, we demonstrated a rare mono-nuclear salen-Al complex that can prompt the ROP of (macro)lactones with unprecedentedly high efficiency. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 973-981