A process for the production of polyester comprising at least 80% of an ethylene terephthalate repeating unit using as a starting material an ester compound made mainly of terephthalic acid and ethylene glycol or an oligomer thereof is disclosed. This process is characterized in that a prepolymer having an intrinsic viscosity of not more than 0.4 dl/g and a carboxyl terminal group concentration [COOH] of not more than 90 x [η] -0.4 µeq/g is fed to a final polymerization unit and polymerized in the form of a molten thin film having a thickness of from 0.005 to 0.15 mm.