The hydrolytic depolymerization of poly(ethylene terephthalate) (PET) was carried out in a stirred batch reactor at 235, 250, and 265 degrees C above its melting point and under autogenous pressure. The solid products which were mainly composed of terephthalic acid were analyzed by potentiometric titration and elemental analysis. The liquid products which were mainly composed of ethylene glycol and a small amount of its dimer were analyzed by gas chromatrography. A kinetic model consisting of forward and backward reactions for the PET hydrolysis fitted well with the experimental data. Moreover, an autocatalytic mechanism was suggested, which indicates that some of the hydrolytic depolymerization of PET was catalyzed by the carboxyl groups produced during the reaction. The dependence of the rate constant on the reaction temperature was correlated by the Arrhenius plot giving the activation energy of 123 kJ/mol for the PET hydrolysis.