A series of chitosan-Zn (II) complexes were synthesized by reaction of chitosan and ZnSO4 in different ratios(chitosan : Zn (II) = 1 : 0.05-1 : 1) in dilute formic acid aqueous solution. The results showed that -NH2, -OH and -NHCO- of chitosan molecule were coordinated to Zn (II) based on the analyse of the IR spectra of chitosan, chitosan-H2SO4 and chitosan-ZnSO4. SO4(2-) of chitosan-ZnSO4 may be crosslinking of chitosan molecule, but Cl-, CH3COO- and NO3- were not crosslinked to chitosan molecule in the chitosan-ZnCl2, chitosan-Zn (CH3COO)2 and chitosan-Zn (NO3)2 complexes.