Drug delivery system using functional nanoparticle is a promising way for the reduction of side effects and the sustained release. Poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles with size 80 nm were prepared through emulsification-diffusion method using Poloxamer 188 as a stabilizer. The prepared nanoparticles have the hydrophobic core for drug loading and the hydrophilic surface corona for avoidance of reticuloendocellial system (RES). First example of biomedical applications is the localization of PLGA nanoparticle containing estrogen for the inhibition of restenosis after balloon injury. In vivo study demonstrated that locally delivered PLGA nanoparticles with estrogen drastically decrease the degree of neointimal formation. Secondly, bone-specific drug delivery was carried out using PLGA nanoparticles modified with alendronate which have a high affinity to bone. It was shown that PLGA nanoparticles conjugated with bisphosphonate were accumulated into bone after intravenous administration into rats.