The present work shows that the enzyme mediated ring-opening polymerization Of L-lactide at 65 degrees C can be achieved using supercritical carbon dioxide. it is reported a biphasic media system where the supercritical phase coexists with a liquid organic phase, which is mainly composed of melted monomer, wherein the growing poly-L-lactide chains are soluble. The immobilized lipase B from Candida antartica was used as the biocatalyst. The results indicated that semi-crystalline polymers with a molecular weight (M-w) up to 12,900 g mol(-1) can be attained and that the monomer conversion is related to the biocatalyst concentration and its initial water activity (a(wi)). Experiments carried out with denatured enzyme gave no monomer conversion which confirms that the enzymatic mechanism is only involved in our system. (C) 2009 Elsevier B.V. All rights reserved.