Aliphatic dithiol-diacid type polythioesters were first enzymatically prepared by the direct polycondensation of hexane-1,6-dithiol and diacid diesters using the immobilized lipase from Candida antarctica (lipase CA). As a typical example, diethyl sebacate and hexane-1,6-dithiol were polymerized using lipase CA in bulk in the presence of molecular sieves 4A to produce the corresponding polythioester with an (M) over bar (w) of 10 200 in 90% yield. Both the melting and crystallization temperatures of the produced polythioesters were higher when compared to those of the corresponding polyoxyesters. A higher molecular weight polythioester was produced using lipase in a two-step procedure, i.e., cyclization with subsequent ring-opening polymerization.