In this study, we attempted to elucidate the Brittle-ductile transition (BDT) behavior of poly(ethylene terephthalate) (PET)/poly(ethylene-octene) (POE) blends under different situations of interfacial compatibility and test temperature. To modulate the compatibility between PET and PEO, maleic anhydride grafted POE (mPOE) was selected as compatibilizer. Three kinds of elastomeric additives, 100 % POE, mPOE/POE (15/85 w/w), and 100 % mPOE, were blended with PET, resulting in three compatibility situations, namely, poor, moderate, and strong interfacial adhesion, respectively. The impact toughness as a function of elastomer content was measured under different interfacial adhesions and test temperature, and microscopic morphology was revealed by scanning electron microscopy and transmission electron microscopy. The results indicated that the interfacial adhesion determines the fashion of microvoiding and even the matrix shear yielding deformation, which will significantly affect the BDT behavior and its response to test temperature. Our study provides not only an effective route to prepare supertoughened PET blends (improved for 20 folds as comparing to the neat PET), but also a fresh insight into the importance of interfacial adhesion on the toughening of thermoplastic/elastomer system.