Lipase from Candida sp.99-125 catalyzed ring-opening polymerization of e-caprolactone in the presence of 6-mercapto-1-hexanol was presented as a new metal-free approach for direct synthesis of welldefined thiol-terminated poly(e-caprolactone).Remarkably,high chemoselectivity of lipase from Candida sp.99-125 toward hydroxyl and thiol was exhibited and quantitative thiol fidelity over 90% was achieved.The tedious protecting/deprotecting steps for thiol and metal residue were avoided.The polymerizations with around 70% monomer conversion were conducted in bulk and toluene at relative low temperature of 40 8C.Number–average molecular weight of resulted polymers ranged from 3000 to4700 Da by changing the feed ratio between monomer and initiator.The structures of obtained thiolterminated poly(e-caprolactone) were demonstrated by combining NMR and SEC analyses. Lipase from Candida sp.99-125 catalyzed ring-opening polymerization of e-caprolactone in the presence of 6-mercapto-1-hexanol was presented as a new metal-free approach for direct synthesis of welldefined thiol-terminated poly (e-caprolactone ). Remarkably, high chemoselectivity of lipase from Candida sp. 99-125 toward hydroxyl and thiol was exhibited and quantitative thiol fidelity over 90% was achieved. The tedious protecting / deprotecting steps for thiol and metal residue were due. The polymerizations with around 70 % monomer conversion were conducted in bulk and toluene at relative low temperature of 40 8C.Number-average molecular weight of formulating polymer ranged from 3000 to 4700 Da by changing the feed ratio between monomer and initiator. The structures of obtained thiolterminated poly (e-caprolactone ) were said by containing NMR and SEC analyzes.