The dynamics of chitosan (CS) in solution have been studied by H-1 NMR relaxation [longitudinal (T-1) and transverse (T-2) relaxation times and NOE] as a function of the degrees of acetylation (DA, 1-70) and polymerization (DP, 10-1200), temperature (278-343 K), concentration (0.1-30 g/L), and ionic strength (50-400 mM). This analysis points to CS as a semirigid polymer with increased flexibility at higher DA in agreement with reduced electrostatic repulsions between protonated amino groups.