PURPOSE: A heat-resistant aromatic polyester which can be produced in an industrially advantageous manner, comprising two specified kinds of structural units and having a specified reduced viscosity.

CONSTITUTION: A polyester comprising structural units of formula I (wherein A is O or S, and R1WR16 are each H, a halogen, or the like) and structural units of formula II (wherein B is O, S, or the like, and R11WR24 are each H, a halogen, or the like). In said polyester, the ratio of structural unit I to structural unit II is 95:5W 5:95 by mole, and the reduced viscosity ηsp/C (as determined at 30°C in a phenol/tetrachloroethane (1:1) mixture and a concentration of 1.0g/dl is 0.1dl/g. Preferably, in formulas I and II, R1WR16 are each H, R17WR24 are each H, A is O and B is analkylidene group. This aromatic polyester can be produced by any of interfacial, solution or melt polycondensation processes.