Abstract: The uptake of Cu(Ⅱ) on chitosan is corresponding to the monolayer adsorption model at 30.0℃ and the equilibrium concentration of Cu(Ⅱ) is less than 61.1 mg dm~(-3). When the pH values are 6.00 and 4.88 respectively, the saturated specific adsorption amounts are kept constant, 26.5 mg·g~(-1), but the adsorption constants are dropped down from 0.202 to 0.0491 dm~3·mg~(-1). It means that an acidized solution may cause the desorption of Cu(Ⅱ) from chitosan uptaken the ions before. Chitosan is very stable at pH～2 by using a 2.5 mol·dm~(-3) acidized NaCl solution because the ionic strength of solution is high enough to prevent the swelling of chitosan. The effect of pH of 0.2 mol·dm~(-3) acidized NaCl solutions on the desorption percentage of Cu(II) from samples used is determined, and the desorption percentage is found to be 81.5% when pH is 3.87.