Amphiphilic diblock copolymers based on methoxy poly(ethylene glycol) (MePEG) and glycolide with different molar composition were synthesized by bulk polymerization without any catalysts. Using diblock copolymers, we have prepared indomethacin-loaded polymeric nanospheres by forming a micelle in selective solvents. The size of nanospheres measured using dynamic light scattering exhibited a narrow monodisperse size distribution and an average diameter in the range of less than 200 nm. The critical micelle concentration (CMC) of MG70 sample determined by fluorescence spectroscopy was 1.57 x 10(-7) mol/l which was lower than the CMC of common low molecular weight surfactant. In vitro release experiments using indomethacin-loaded MePEG/glycolide nanospheres exhibited the sustained release behaviour without any burst effect. In addition, the results of cytotoxicity tests using an MTT assay method showed that these MePEG/glycolide nanospheres could remarkably reduce cell damage compared with unloaded free drug.