Waste Poly(butylene terephthalate), PBT powder was depolymerized in nitric acid under various temperatures below its melting temperature at atmospheric pressure. The kinetics of the hydrolysis of PBT could be explained by a modified shrinking core model, in which the effective surface area is proportional to the degree of unreacted PBT, (1-XB), affected by the deposition of TPA. The activation energy of the hydrolysis was 98.04 kJ/mol. The recovery ratio was about 93%.