A series of acylated chitosans were synthesized by reacting chitosan with hexanoyl, decanoyl, and lauroyl chlorides. The chemical structures of these polymers were characterized by elemental analysis, IR, H-1-NMR, C-13-NMR, and GPC. These results suggested that the degree of substitution was 4 per monosaccharide ring. These acylated chitosans exhibited an excellent solubility in organic solvents such as chloroform, benzene, pyridine, and THF and transparent films were obtained from these solutions. Dynamic mechanical analyses (DMA) showed that all acylated chitosans have two phase transitions in the solid state. The first transition at -10, -42, and -40 degrees C are attributable to the glass transition (T-g) of H-, D-, and L-chitosans, respectively. The second one around 88 degrees C may be attributed to the transition related to the structure formed by the side chains. WAXS analyses indicate that these polymers form a layered structure in solid state and the layer spacing d increases linearly with increasing the length of side chains.