A series of poly(L-lysine)s grafted with aliphatic polyesters, poly(L-lysine)-graft-poly(L-lactide) (PLy-g-PLLA) and poly(L-lysine)-graft-poly(F-caprolactone) (PLy-g-PCL), were synthesized through the Michael addition of poly(L-lysine) and maleimido-terminated poly(L-lactide) or poly(epsilon-caprolactone). The graft density of the polyesters could be adjusted by the variation of the feed ratio of poly(L-lysine) to the maleimido-terminated polyesters. IR spectra of PLy-g-PCL showed that the graft copolymers adopted an alpha-helix conformation in the solid state. Differential scanning calorimetry measurements of the two kinds of graft copolymers indicated that the glass transition temperature of PLy-g-PLLA and the melting temperature of PLy-g-PCL increased with the increasing graft density of the polyesters on the backbone of poly(L-lysine). Circular dichroism analysis of PLy-g-PCL in water demonstrated that the graft copolymer existed in a random-coil conformation at pH 6 and as an alpha-helix at pH 9. In addition, PLy-g-PCL was found to form micelles to vesicles in an aqueous medium with the increasing graft density of poly(epsilon-caprolactone). (c) 2006 Wiley Periodicals, Inc.