The paper presents the mechanism of lactide polymerization initiated with zinc (II) acetylacetonate monohydrate. However, the actual initiator of this reaction is the complex containing a metal-oxygen bond, formed by the exchange reaction of acetylacetonate ligand with deprotonated lactide derivative. The described reaction results in the release of free acetylacetonate and formation of transitional zinc complex with metal-oxygen bond connecting the zinc atom with derivative of lactide, incorporated - as a new, active in polymerization ligand. Polylactide chain propagation process, which constitutes the following stage of the reaction, is caused by a typical, well known, coordination-insertion ring opening polymerization. The proceeding polymerization maximum yield at the applied conditions does not exceed about 70% in benzene solution and 90% at bulk. (C) 2011 Elsevier Ltd. All rights reserved.