PURPOSE: A novel polyester imide consisting of a specific structural unit, showing liquid crystal in a molten state, modable in a molten state, having low anisotropy of physical properties of molded article, having improved physical properties.

CONSTITUTION: A polyester imide substantially consisting of the structural units A, B, and C shown by the formula I , formula II, and formula III, respectively, having substantially equimolar amounts of the unit B and the unit C, containing 20W40mol% unit A, having at least 0.4dl/g logarithmic viscosity. This polyester imide has characteristics of possession of the unit shown by the formula III, the unit C has a hydroxyl group contributing to bond is in a unsymmetrical position based on the main chain of the prepared high polymer, it eases symmetry of molecular structure produced from the unit A and the unit B, the imide bond in the unit C is expected to have intermolecular mutual action better than ester bond, and provides a molded article having low anisotropy of physical properties.