Conditions for polymerizing ethylene terephthalate cyclic oligomers (ETCs) with the catalyst antimony trioxide were investigated with the ultimate goal in mind of using ETCs to produce highperformance poly(ethylene terephthalate) (PET) composites. The ETCs used were prepared both by a direct synthesis method and by cyclodepolymerization (CDP) in dilute solution. ETCs prepared exhibited a distribution of oligomeric species displaying a broad melting range, the uppermost end of which lies at 290 degrees C. In the case of ETCs prepared by CDP, purified ETCs (p-ETCs) were prepared by eliminating remaining impurities including linear oligomers and cyclic oligomers containing the diethylene glycol (DEG) unit using dichloromethane and tetrahydrofuran. A homogeneous mixture of ETCs prepared by the direct synthesis method or p-ETCs with antimony trioxide was successfully polymerized to I high molecular weight (MW) PET (M-n greater than or equal to 25 000) at 293 degrees C within 15 min. The lower the contents of remaining impurities, the higher the MW of the resultant PET. The PET of highest: MW (M-n = 32 000) was obtained from polymerization of p-ETCs with bismuth trioxide at 293 degrees C for 15 min. PET polymerized from p-ETCs showed the same thermal behavior as did the commercial one. In this research, a useful method of PET recycle by using ETCs was successfully established.