The nucleation effect of the alpha-cyclodextrin (alpha-CD)-polyester inclusion complex (IC) on the crystallization of semicrystalline aliphatic polyesters has been studied in the previous work, in which it was revealed that the effectiveness of alpha-CD ICs as a nucleating agent of aliphatic polyesters is mainly governed by the kinds of polyesters and the host-guest stoichiometry of alpha-CD-polyester ICs [Dong et al., Macromolecules 2005, 38, 7736; 2006, 39, 2427]. In this work, the effects of host-guest stoichiometry of alpha-CD-polymer ICs and molecular weight of guest polyesters on the crystallization behavior of polyesters were further studied by differential scanning calorimetry and polarized optical microscopy. As the guest polymers, two kinds of linear aliphatic polyesters, poly(epsilon-caprolactone) (PCL) and poly(butylene succinate) (PBS) with high and low molecular weight, were used. The ICs with various host-guest stoichiometry between alpha-CD and polyesters were successfully prepared, and they used as the nucleating agents for crystallization of PCL and PBS. It was found that the host - guest stoichiometry of ICs affects their nucleation ability on the crystallization of polyesters, and these ICs with about 30-70% uncovered parts showed most effective. Furthermore, the molecular weight of guest polymers also favorably affected their IC's nucleation ability on crystallization of polyesters. This research will be give us the route of making an effective green nucleating agent for bio-based polymer.