The viscosity properties of diluted chitosan solutions in 2% and 70% acetic acid and sodium acetate buffer (1.9% CH3COOH + 1.6% СН3СООNа) within 25–70°C were studied. Concentra- tion dependences of the viscosity number were plotted. Intrinsic viscosities, Huggins’ constants and the temperature coefficients of viscosity were estimated. The intrinsic viscosity of solutions of this aminopolysaccharide in acetic acid has been found to be significantly higher than that in acetate buffer.