Enzymatic ring-opening polymerization of a 6-membered cyclic carbonate, 1,3-dioxan-2-one, was investigated by using lipase as catalyst in bulk. Supported lipase derived from Candida antarctica catalyzed the polymerization to give the corresponding aliphatic polycarbonate. Unchanged monomer was recovered in the absence of the enzyme or using an inactivated enzyme, indicating that the present polymerization proceeds through enzymatic catalysis.