The polyesters such as polylactide or poly(D,L-lactide-co-glycolide) was approved as a biodegradable and biocompatible polymer for clinical uses by Food & Drug Administration (FDA) in USA. In this case, we can observe that poly(ethylene oxide) drifts to the surface of nanoparticles by phase separation and drug concentration effused in blood increases in comparison with that case when polymer parti