Thermotropic behavior of hydroxyethyl cellulose acetate (HECA) was studied by polarizing microscopy, DSC, and X-ray diffraction. It was found that HECA was an anisotropic liquid between the temperature from 130 to 185-degrees-C on heating, and when the temperature was over 185-degrees-C, it became isotropic. In cooling, however, mesophase began to form at about 165-degrees-C. The transformation temperature decreased with decreasing molecular weight and the temperature region of transformation decreased with decreasing the distribution of the molecular weight for HECA. The kinetic ability of transformation appeared the maximum with molecular weight. The HECA liquid crystal is cholesteric and the distance between layers of ordered molecular chains was enlarged when HECA was transformed from liquid crystalline glass to the liquid crystalline state.