Copolymers Of poly(L-lactic acid) and methoxy end-capped poly(ethylene glycol) were synthesized, and their structure and physical properties were characterized. Micellar structures were formed in aqueous media because of the amphiphilic nature of the copolymers, and their sizes were measured with both dynamic light scattering equipment and scanning electron microscopy. Indomethacin was loaded into the copolymer micelles, and its releasing behavior was monitored. The drug-releasing mechanism was determined from an investigation of the biodegradation kinetics of the copolymer micelles. The releasing mechanism was governed by diffusion rather than a biodegradation process. We adapted a model based on Fick's diffusion theory to describe the overall releasing behavior with the extraction of the diffusion coefficient. (C) 2001 John Wiley & Sons, Inc.