Abstract: Organosoluble hexanoyl chitosan(HC) was synthesized through esterification reaction between chitosan and hexanoyl chloride in methylsulfonic acid solutions. This intermediate was further PEGylated through NHSDCC coupling method to give PEG-g-HC. The chemical structure of HC and PEG-g-HC were characterized by FT-IR, 1H-NMR and UV-Vis． The selfassembly behavior of PEG-g-HC was studied by DLS, fluorometer and TEM. The degree of substitution(DS) of HC can be adjusted by varying the feed ratio of hexanoyl chloride to chitosan. The critical pH at which HC could be soluble in aqueous media increased with the increase of DS of HC. Spherical micelles with pH responsibility could be formed through selfassembling of PEG-g-HC in aqueous media. In addition, the critical pH where the micelle size abruptly decreased could also be modulated by varying the DS of HC.