Viscosity variation ensuing from processing temperature and time elapsed in acetic solution of chitosan was investigated by rotary viscometer. The solution showed a typical behavior of pseudoplastic liquid where the gradient of shear stress decreases as strain rate increases. The apparent viscosity decreased as chitosan polymer degraded with temperature rise and time elapsed in the solution. And the decrease in viscosity occurred rapidly in a fixed time interval at each temperature. The proportionality of viscosity to temperature was confirmed by temperature superposition curve that was obtained with the temperature dependence shift factor a$_{T}$ in WLF equation. Intrinsic viscosity was linearly proportional to apparent viscosity within a fixed range depending on strain rate. The activation energy of chitosan was about 55.2 KJ/mole in the acetic solution, which was calculated from intrinsic viscosity based on the Andrade-Eyring equation.n.