Free amino groups in beta-chitin from squid pen were acetylated to obtain N-acetylated beta-chitin. After careful control of degree of acetylation, thermal and mechanical properties of beta-chitin and N-acetylated beta-chitin were compared. The structural differences of beta-chitin and N-acetylated beta-chitin were characterized by Fourier transform infrared (FTIR) and wide-angle x-ray diffraction (WAXD) analysis. The results indicated that the crystallinity of N-acetylated beta-chitin was higher than that of beta-chitin and N-acetylated beta-chitin exhibited characteristics similar to alpha-chitin. Equilibrium water content (EWC) of beta-chitin reached to about 50% and this hydrophilic nature was assumed to be caused by a relatively weak hydrogen bonding force of beta-chitin with parallel main chains. On the other hand, EWC of N-acetylated beta-chitin was 40% due to the introduction of ordered structure. beta-chitin and N-acetylated beta-chitin have the tensile strength of 0.4 and 0.7 Mpa in the swollen state, respectively. Viscoelastic properties and thermal relaxation behaviors were investigated by dynamic mechanical thermal analysis (DMTA). DMTA spectra of these samples showed that alpha-transition peaks of beta-chitin and N-acetylated beta-chitin were observed at 170 and 190 degrees C, respectively. These relaxation peak maxima were assigned to be their glass transition temperature. In addition, a second relaxation peak of beta-chitin resulting from acetamide groups was found at 112 degrees C and a broad relaxation peak of N-acetylated beta-chitin at around 81-100 degrees C. As a result of thermogravimetric analysis, 10% weight loss temperatures of beta-chitin and N-acetylated beta-chitin were 270 and 285 degrees C, respectively.