Summary: Polyesters and polyolefins form highly incompatible blends with poor properties and gross morphology that hinder any practical applications. In this work, the possibility to compatibilize an incompatible blend of poly(butylene terephthalate) (PBT) with ethylene vinyl acetate (EVA) by adding a bis‐oxazoline compound, 2,2′‐(1,3‐phenylene)‐bis(2‐oxazoline) (PBO), and an ethylene acrylic acid copolymer (EAA) as compatibilizer precursors has been studied. The results indicate that the binary uncompatibilized blends show poor mechanical properties and a bad morphology with scarce adhesion between the phases. The situation is only slightly improved when the EAA is added while the best performance is achieved when quaternary PBT/EVA/EAA/PBO blends are prepared. In this latter case the elongation at break and the impact strength are doubled and the morphology is deeply improved. The formation of EAA‐g‐(PBO)PBT copolymers in the presence of PBO can be invoked to explain the results and it is demonstrated that the eventual chain extension of PBT or EAA is negligible.