In attempts to improve the thermal and mechanical properties of polyethylene terephthalate/polycarbonate (PET/PC) blends nanofil 9 was used. Blending was carried out in a Brabender plasticorder, the chopped composites were then extruded using a single screw extruder to prepare samples for the thermal and mechanical testing. Lanthanum acetyl acetonate hydrate was used as a catalyst for potential transesterification reactions that could occur in the melt. PET/PC nanocomposites were characterized through polarized light microscopy, differential scanning calorimetry, and for mechanical properties. The required torque is reduced as the amount of the nanofiller increases, the presence of the catalyst in addition to nanofil 9 reduced the viscosity of the composites. The addition of nanofil 9 to the PET did not change the glass transition temperature, while the crystallization temperature of the PET shifted to a higher value. On the other hand, the introduction of the nanofil 9 slightly decreased the melting temperature.PET/PC blends are completely immiscible over the composition range covered; there are two values for the Tg independent of composition. These two Tg values are very close to each other for PET/PC blends prepared with added catalyst. As the percentage of PC increased, the crystallization temperature increases while the melting temperature decreases. A maximum value for the Young's modulus obtained for both the virgin PET and the PET/PC nanocomposites filled with 1 to 2 wt% nanofil 9. Also, the virgin PET and the PET/PC nanocomposites become very brittle as the percentage of the nanofil 9 increases.