Abstract: The relative molecular weight of chitosan was determined by the relationships of three methods, HPLC, intrinsic viscosity, and dynamics viscosity. The intrinsic viscosity of chitosan solution was measured with one-point Ubbelohde viscometer, the relative molecular weight of chitosan was determined with HPLC, and the MHS equation was obtained as [η] = 3.72 × 10－5Mw 1.37. This paper also sets up the relationship between dynamics viscosity and the molecular weight of chitosan during 10 mg/mL solution degradation by chitosanase.