A series of low molecular weight chitosans (LMWCS) with different molecular weight and lower polydispersity were prepared by the degradation of high molecular weight chitosan with H2O2/CH3COOH and gradient ethanol solution treatment. Fourier transform infrared spectra （FTIR）and 13nuclear magnetic resonance spectroscopy (13CNMR) analysis showed that the structure of the prepared LMWCS was similar to that of original chitosan without any significant change. X-ray diffraction (XRD) measurements indicated that, with the decrease of the molecular weight, the pattern transformed from "L-2 polymorph"(original chitosan) to a mixture of "annealed polymorph" and "tendon hydrate polymorph", and finally tended to amorphous. Cell culture experiments in vitro suggested that, the prepared LMWCS, in low concentrations, promoted the proliferation of fibroblasts; however, the monomer of chitosan (D-glucosamine, GlcN) had cytotoxicity in the concentration of 1 mg/ml.
