In order to improve the mechanical performance of polycarbonate (PC), different contents of poly(ethylene-2,6-naphthalene) (PEN) were blended with PC, and ethylene-methyl acrylate- glyceryl methacrylate terpolymer (E-MA-GMA) was selected as compatibilizer. The different PC/PEN composite were then prepared by conventional injection molding, and tested for tensile properties at two test speeds. The samples were further characterized by differential scanning calorimetry (DSC), dynamic thermomechanical analysis (DMA), and scanning electron microscopy (SEM). It is found from the tensile testing that the mechanical performance can be improved obviously with the addition of PEN. The influence of PEN on the mechanical performance is most remarkable when the ratio of PC and PEN is 25%. It is also found that there is a relationship between the mechanical performance and the compatibility of two phases of the composites. The phenomenon of the strain harden could be observed for the composites, especially, the addition of E-MA-GMA, which resulting in a great increase of the break strength and the strain-at-break. Furthermore, the mechanism of performance improvement was studied by SEM observation, DSC analysis, and DMA test. The results show that the improvement of mechanical performance can be attributed to the stable fiber-shape structure which is formed in the process of the tensile test.