Water-insoluble triblock poly(caprolactone-b-ethylene oxide-b-caprolactone) (PCL-PEO-PCL) was micronized into narrowly distributed nanoparticles stable in water. Using a combination of static and dynamic laser light scattering (LLS), we characterized the resultant nanoparticles and studied their biodegradation in the presence of enzyme lipase PS. The results revealed that the biodegradation rate was mainly dependent on the enzyme concentration. The scattering intensity decreased as the degradation proceeded, but there was no change in size of the remaining nanoparticles, indicating that the degradation of each particle was fast and the enzyme consumed the nanoparticles individually. We also found that different copolymer compositions, i.e., different PCL-PEO molar ratios, led to different biodegradation rates. The pH and temperature dependence of the biodegradation rate were also studied. All results indicated that the biodegradation rate can be well controlled and the biodegradation essentially involves two processes: adsorption of lipase PS onto the nanoparticles, and enzymatic hydrolysis of the PCL blocks. The biomedical application of the enzymatic biodegradation of the copolymer nanoparticles is also envisioned.