Abstract: Chitosan nanoparticles encapsulating recombinant human endostatin (Endostar) were prepared by the ionic gelation process.Characterizations including drug loading,encapsulation efficiency,particle size,morphology,in vitro release,bioactivity and the integrity of Endostar were investigated.It was found that drug loading and encapsulation efficiency were (10.5±1.1)% and (81.3±1.8)%,respectively.The average particle diameter of the spheric nanoparticles was 137 nm.80% of cumulative release was achieved after 10 d.The results of SDS-PAGE indicated no change to the structure of Endostar during the process of preparation and in vitro release.The endothelial cell proliferation assay showed that the nanoparticles retained the bioactivity of the protein.These results indicated that Endostar nanoparticles prepared with chitosan possessed appropriate particle size and encapsulation efficiency,exhibited sustained release in vitro,maintained the structure of Endostar,and retained the bioactivity of the protein.