Dynamic and static light-scattering experiments were performed on aqueous solutions of the highly charged semiflexible polyelectrolyte chitosan in the dilute and the semidilute regime. In the dilute regime, typical good solvent behavior is found. However, in the overlapped regime the time autocorrelation function of the scattered electric field is found to be bimodal. The short lime relaxation has a typical q(2) dependence, characteristic of diffusion, and the long time relaxation an approximately q(2) dependence, where q is the scattering wave vector. Static and dynamic light-scattering experiments were carried out to analyze the two modes. The fast mode is attributed to the relaxation of concentration fluctuations characterized by a cooperative diffusion mechanism of the polymer network meshes. The slow relaxation time appears to be related to the diffusion of polymer associations. The effect of the excess of salt concentration and polymer concentration was investigated.