Abstract: Phthaloyl chitosan,an important chitosan derivative,has been used in many fields especially as an intermediate for further modification of chitosan.Several samples with different degree of substitution were synthesized from completely deacetylated chitosan at room temperature.Only amic acid-chitosans were found in these product instead of both amic acid-chitosan and imide-chitosan that were found at ri rous high temperature (more than 130 ℃) as reported by others.XPS was used to measure the degree of substitution.From the measurement,it was shown that the substitution happened at either N atom or O atom of the glucosamine units.As the dosage of phthaloyl anhydride changed,degree of substitution on N atom (dsN) remained almost unchange (0.26±0.03) while degree of substitution on O atom (dsO) varied from 0.01 to 1.54.PhCS can dissolve in several common organic solvents such as DMSO,dichloroacetic acid (DCA),formic acid (FA) etc and forms lyotropic mesophases.Their critical concentrations (c) were determined in some of the above solutions.The dsO showed only slight effects on c.The results were consistent with previous studies on other systems of chitosan derivatives.