Photocrosslinkable chitosan（Az-HPCS） was prepared by introducing Az-group onto the amino group of a water-soluble chitosan derivative

hydroxylpropyl chitosan（HPCS）.The chemical structure and substitution degree of Az-HPCS were FTIR

NMR and amino-group titration methods.Chitosan nanogel was then prepared by ionic-crosslinking followed by photocrosslinking.The morphology and size of the yield nanogel was then characterized by TEM.Furthermore

the swelling degree

entrapment efficiency and drug releasing hehavior were studied as well.It was found that the entrapment efficiencies of the nanogel at different pH were similar

while the swelling degree and releasing behavior were related to the pH of the enviroment.At pH 2.60

the nanogel has the highest swelling ratio（80%）

and the loaded drug was burst released in the beginning 30 minutes.At pH 9.40

nanogel has the lowest swelling ratio

and only release 40% of the drug in 2 hours.However

in neutral condition（pH 7.38）

the nanogel showed great controlled releasing property.