This study was focused on thermal degradation behavior of PET/PTT polymer blends, which were blended with different weight ratios of PET and PTT homopolymers. Thermal degradation behavior was observed using a Thermogravimetric Analyzer (TGA). The degradation activation energy was calculated by a Doyle-Ozawa equation. The results showed that the thermal degradation temperature of the blended PET/PTT decreased with an increase of PTT content. In addition, the degradation activation energies of the PET/PTT polymer blends were between that of two homopolymers.