An aliphatic polyester with free pendant mercapto groups was prepared by direct lipase-catalyzed polycondensation of hexane-1,6-diol and dimethyl 2-mercaptosuccinate. The polycondensation reaction using immobilized lipase from Candida antarctica (lipase CA) was carried out in bulk at 70 degrees C without any formation of disulfide or thioester linkages to produce the corresponding polyester with M-w = 14000 g/mol in high yield. The content of free mercapto groups in the polyester could be controlled by copolymerization with other monomers. The obtained polyester was easily cross-linked to form gels by the air oxidation of the pendant thiols to disulfides in dimethyl sulfoxide.