Abstract The thermal properties of chitin and hydroxypropyl chitin (HPCH) were examined. Hydroxypropyl chitin was prepared from chitin and propylene oxide. The structure of HPCH was confirmed by solid-state 13 C nuclear magnetic resonance and Fourier-transform infra-red spectroscopy. From the results of elemental analysis, the degree of substitution was revealed to be about 0.8. As hydroxypropyl moieties were introduced on the C6 position in chitin, the solubility of HPCH in many organic solvents was enhanced compared with that of chitin. The dynamic mechanical analysis (d.m.a.) technique was employed to ascertain the glass transition temperature ( T g ) of chitin and HPCH. The α transition peak of cast chitin and HPCH film by d.m.a. was observed at 236 and 252°C, respectively. Considering that rigid-rod-type polymers show T g followed by rapid thermal degradation, it was proposed that these temperatures should be T g . Moreover, β relaxation peaks were detected at ca. 143°C attributed to the presence of acetamide groups in chitin. In the d.m.a. spectra of HPCH, a new tan δ peak, β 2 relaxation behaviour, was found at 105°C, probably due to the relaxation of the hydroxypropyl moiety in HPCH. Weight loss by thermogravimetric analysis implied that the relaxation above 250°C resulted from the decrease in modulus and was caused by thermal decomposition.