Transition-metal-substituted polyoxometalates (POMs) K6SiW11MO39(H2O) (M = Zn2+, Mn2+, Co2+, Cu2+, Ni2+) show excellent catalytic activities in the glycolysis of poly(ethylene terephthalate) (PET) under mild conditions. The effects of temperature, catalyst amount and reaction time on PET degradation are investigated. The PET could be fast and completely degraded at low catalyst/PET molar ratio (0.13%) and high PET/EG weight ratio (1:4). The yield of bis(hydroxyethyl) terephthalate (BHET) exceeds 84% with the SiW11Zn as the catalyst under atmospheric pressure at 185 degrees C for 30 min. The catalyst and ethylene glycol (EG) can be easily separated from the products by filtration and can be reused together. After recycling eight times, the conversion of PET and the yield of BHET can still reach 100% and 83%, respectively. The possible nucleophilic substitution mechanism for PET glycolysis using the K6SiW11ZnO39(H2O) as the catalyst is proposed. The POM catalysts are hopeful to provide the possibility for other polymer degradation. (c) 2015 Elsevier Ltd. All rights reserved.