Abstract: The process of phase separation for a new thermoplastic polyurethane/poly (ethylene-octene) (TPU/POE) blending system was studied by Fourier Transform Attenuated Total Reflection Infrared Spectroscopy (ATR-FTIR). The results show that, for the incompatible TPU/POE system, the area of characteristic peak on ATR-FTIR increased with the increase of thermal aging time (except at quite low temperatures), while it increased first and then decreased at higher temperatures. For a PU/POE/POE-g-MA system, the area decreased due to the addition of compatibilizers.