AbstractThis paper presents information on the preparation of the network polyester films from glycerol (Yg) and aromatic dicarboxylic acids of phthalic anhydride (P), dimethyl isophthalate (I) and dimethyl terephthalate (T), as well as aliphatic dicarboxylic acids of adipic, sebacic, 1, 10‐decanedicarboxylic and 1, 12‐dodecanedicarboxylic acids, and their properties. Ygand dicarboxylic acid were polycondensed immediately before the gelation started. The prepolymers obtained were cast from DMF solution and successively post‐polymerized at various temperatures and times to form networks. The resultant films were transparent, flexible and insoluble in organic solvents. Heat distortion temperature (Th) measured by a penetration mode of thermomechanical analysis increased with increasing post‐polymerization temperature and time, and then leveled out.Thvalues corresponded well to the glass transition temperature (Tg) measured by differential thermal analysis (DTA).Thwas 152°C, 162°C and 197°C for YgP, YgI and YgT post‐polymerized at 270°C for 6 h, respectively.Thvalues of network films made from aliphatic dicarboxylic acids could not be observed until complete probe penetration occurs, as a result of thermal decomposition because theTgis lower than room temperature. The degree of reaction estimated from the IR absorbance of hydroxyl and methylene groups was in the range of 60–80%. Two diffraction peaks appeared in the wide‐angle X‐ray scattering pattern, suggesting some ordered structure owing to the regular networks. Density decreased with increasing post‐polymerization time and temperature, in the order YgP>YgI>YgT. Network films made from aliphatic dicarboxylic acids had much lower tensile strength and Young's modulus, and greater elongation, than those made from dicarboxylic acids, as a result of theTgbeing b