The effectiveness of graphene oxide (GO) as reinforcement material and Joncryl as compatibilizing agent for poly(ethylene terephthalate) (PET)/poly(butylene terephthalate) (PBT) blend was evaluated. The blend and its nanocomposites were produced via melt extrusion and injection molding. Properties of the produced samples were explored by using Fourier transform infrared spectroscopy, scanning electron microscope (SEM), melt rheological measurements, dynamic mechanical analysis, and tensile test. While there was no interaction between GO and PET/PBT, the addition of Joncryl to nanocomposites resulted in possible ring-opening reactions. SEM images showed that all nanocomposites were brittle and agglomerated while the PET/PBT matrix showed a ductile structure. The GO and Joncryl addition enhanced the viscoelastic properties of the PET/PBT. The tensile strength and elongation at break values of PET/PBT, decreased with the addition of GO, indicates weak interfacial adhesion. Joncryl has developed the mechanical properties by compatibilizing PET/PBT and GO.