Aliphatic polyesters such as polylactide (PLA), polyε-caprolactone (PCL).. and their copolymers are among the most promising biodegradable polymers. They are biocompatible, enzymatically and chemically degradable and bioresorbable due to a total metabolization of the degradation products. PCL in particular is permeable to low molecular mass molecules at human temperature and its rate of degradation is slower than polyglycolide or copolymer of PLA: for these reasons it is the most used for absorbable surgery sutures, orthopedic fixations, and dental cares or for controlled release of bioactive compounds. At industrial level this polymer is readily obtained in a controlled manner via the ring-opening polymerization of ε-caprolactone (CL) using catalysts based on transition and post-transition metals such as tin, aluminum, iron, zinc, bismuth.. The drawback of these homogeneous systems is the contamination of the resulting polyesters by residual metal that have to be avoided for medical use. Therefore organocatalyzed ring-opening polymerization has emerged as a promising alternative to its metal-catalyzed counterpart. Organocatalyzed ring-opening polymerization of lactones was carried out by activation of the electrophilic monomer using a Brønsted acid or a catalytic nucleophile, by activation of the nucleophilic growing polymer chain using a base, or via a dual activation of both reacting species using a thiourea/tertiary amine system or phosphoricor sulfonic acids. Recently, the ring-opening polymerization of lactones and lactides was described in imidazolium based ionic liquids (IL) in the presence of a nucleophilic catalyst (in-situ generated carbine or DMAP), a Lewis acid, tin octanoate or even an enzyme. N,N’-dialkylimidazolium-based ionic liquids were shown to act as catalyst in the polymerization of L-lactic acid oligomers at high temperatures. Herein, we describe the use of ionic liquids as a new metal-free bulk ring-opening polymerization catalyst for CL.