The oxidative ozone treatment of poly (ethylene terephthalate) fibers after dyeing was recently proposed as a novel afterclearing method. High fastness properties, energy and time savings, and environmental benefits were reported by the ozone treatment compared to the conventional reduction clearing. This study investigated the efficiency of the ozone treatment afterclearing process on the surface trimer removal of poly(ethylene terephthalate) fibers. Results indicated similar cyclic trimer [(GT)(3)] removal rates after 1 min ozone treatment when compared to the conventional reduction clearing; the removal rates increased at 3 min ozone treatment time. The migration rate of the cyclic trimers [(GT)(3)] Out Of the fibers was also investigated as a function of temperature and a sudden increase was observed after second glass transition temperature of poly (ethylene terephthalate) fibers rather than a linear increase.