A series of biodegradable graft copolymers composed of poly(ethylene glycol) side-chains and a poly(depsipeptide-co-DL-lactide) backbone (PDG-DL-LA-g-PEG) were prepared as a novel thermo-gelling system. An aqueous solution of PDG-DL-LA-g-PEG (20 wt%) with a certain PEG length and composition showed instantaneous temperature-sensitive gelation at 33 degrees C. The sol-gel transition temperature (T-gel) Could be controlled from 33 to 51 degrees C by varying the PEG length and compositions without a decrease in mechanical strength of the hydrogels. The 20 wt% hydrogel was eroded gradually in PBS at 37 degrees C for 60 days. This research provides a molecular design approach to create biodegradable thermo-gelling polymers with controllable T-gel and mechanical toughness. (C) 2009 Elsevier Ltd. All rights reserved.