The mesophase transition and its kinetics of chitosan in the solutions of chitosan/dichloroacetic acid (DCA) were investigated by means of DSC and depolarized light intensity technique, respectively. The mesophase formation of chitosan in DCA involves nucleation and growth. The isothermal kinetics of mesophase formation from isotropic phase were described by Avrami using the equation with an exponent n close to 1, which suggests that the formation of chitosan mesophase is a process of instantaneous nucleation and one-dimensional rod-like growth in the temperature range investigated. This was confirmed by small angle light scattering Hv patterns of the mesophase.