Water-insoluble poly(ethylene oxide-b-epsilon-caprolactone)(PEO-b-PCL) diblock copolymer (M-w = 1.71 x 10(4) g/mol and W-PEO = 20%) was successfully micronized into small polymeric core-shell nanoparticles (micelles) stable in water via a microphase inversion method. Such formed PEO-b-PCL nanoparticles are biodegradable in the presence of Lipase PS (enzyme). The biodegradation of the PEO-b-PCL nanoparticles, actually, only the hydrophobic PCL core, was monitored by laser Light scattering. The biodegradation extent could he influenced by both the copolymer and enzyme concentrations, while the biodegradation rate was mainly determined by the enzyme concentration. Using pyrene as an imitative drug and fluorescence spectroscopy, we have shown that hydrophobic drugs can be easily loaded into the PCL core in the micronization process, and the biodegradation of the PCL block results in the dissolution of the nanoparticles and the releasing of pyrene molecules because the PEO block is soluble in water. The potential biomedical application of the PEO-b-PCL nanoparticles as a controlled release device has been demonstrated.