In recent years,chitosan microspheres have attracted more and more attention as a carrier for drug delivery because chitosan has good compatibility,biodegradability,and biological adhesion properties.In our study,folic acid conjugated chitosan nanoparticle was developed.Folic acid receptor (FR) is over-expressed in most malignant tumor cells and foLic acid has a high affinity to FR [1].Folic acid is conjugated to the surface of chitosan nanoparticles via its γ-carboxyl moiety and thus retain a high affinity for cancer cells bearing folate receptors [2].The interaction of folic acid with the folate receptor is stable when the pH is ranging from 4.3-6.9.Usually normal tissue and tumor tissues have different pH values,and the extracellular pH of tumor tissues decreases with increase of metabolic activity [3].Therefore,folate targeted nanoparticles can enter efficiently into tumor cells,which leads to selective accumulation.