In order to study the structure and the catalytic activity of aliphatic tertiary amines,the ring-opening polymerizations of trimethylene carbonate(TMC) and L-lactide(L-LA) were catalyzed by aliphatic tertiary amines,including triethylamine(TEA),N,N,N′,N′-tetramethylethylenediamine(TMEDA),1,1,4,7,7-pentamethyldiethylenetriamine(PMDTA) and 4-(dimethylamino)pyridine(DMAP),using benzyl alcohol as initiator in THF at 55℃.Studies revealed the catalytic activity of these tertiary amines was increased according to the order:TEA TMEDA≈PMDTA DMAP.The relationships of polymer molecular weight with the conversion of monomer were linear,which were consistent with a living polymerization character.Finally,the plausible polymerization pathway was through an alcohol-activating mechanism.Aliphatic tertiary amines which were abundant in source and cheap in price were suitable for catalyzing the ring-opening bulk polymerization of lactone in low temperature because of their low boiling point,being liquid under ordinary conditions and being easy to get rid of.