Ring-opening polymerization of lactones initiated by cyclodextrins has been reported as a promising polymer synthetic method. To investigate the unknown molecular level mechanism of the initiation reaction, we executed molecular dynamics simulations of model systems composed of single or multiple beta-cyclodextrin (beta-CD) molecules in delta-valerolactone (VL) solvent and explored the reactant complex structures satisfying three conditions (VL inclusion in the beta-CD cavity, hydrogen bonding, and nucleophilic attack) at the same time. As a result, we confirmed the formation of the reactant complex structure. Comparison between the single and multiple beta-CD models revealed that the formation is more frequent and the distance for the nucleophilic attack is shorter in the multiple model. Therefore, we anticipate that the reaction proceeds more efficiently by the cooperation of multiple beta-CDs. This finding will contribute to understanding the reaction mechanism from the atomistic point of view.