A monometallic (Ni2+, 1) and a series of bimetallic (Ni2+-Ln(3+), Ln = Ce (2); Ln = Nd (3); Ln = Sm (4); Ln = Eu (5); Ln = Tb (6); Ln = Ho (7); Ln = Tm (8)) complexes based on the Salen-type Schiff-base ligand H2L (H2L=N,N'-bis(3-methoxysalicylidene)ethylene-1,2-diamine) were synthesized and characterized by EA, FT-IR, ESI-MS and X-ray crystallography. The catalysis results showed that the two kinds of complexes with different active species, could efficiently catalyze the bulk solvent-free melt ring-opening polymerization (ROP) of L-lactide with moderate molecular weights and narrow molecular weight distributions. Especially for the series of bimetallic complexes 2-8, the involvement of rare ions effectively passivated the catalytic behaviors on the ROP of L-lactide, while was in favor of the increase of polymeric molecular weights (M-w, or M-n) and the polymerization controllability, and the type of rare ions was important and influential factor contributing to the catalytic behaviors. (C) 2011 Elsevier B.V. All rights reserved.