Tn this study, dual compatibilizers composed of styrene maleic anhydride random copolymer (SMA-8 wt.% MA) and poly[methylene (phenylene isocyanate)] (PMPI) have demonstrated to effectively compatibilize the immiscible and incompatible blends of poly(ethylene terephthalate) (PET) and polystyrene (PS). SMA with low MA content is totally miscible with PS to make the PS phase quasi-functionalized, so that PMPI has the chance to contact and react with PET and SMA simultaneously to form PET-co-PMPI-co-SMA copolymers at the interface. These desired copolymers are able to anchor along the interface and serve as efficient compatibilizers. The compatibilized blends, depending on the quantity of dual compatibilizers employed, exhibit higher viscosity, finer phase domain, and improved mechanical properties. Moreover, the crystallization behavior of the PET component in these compatibilized blends has been affected.