In-situ poly (ethylene terephthalate) (PET) nanofibrils were created by drawing of melt blended polypropylene and PET. The drawn blend was used to prepare polymer-polymer nanofibrillar composites (NFCs), in order to compare the effect of different fibril orientations on the mechanical properties. The resulting composites showed excellent improvements in stiffness of 116% vs. the isotropic PP matrix for uniaxial NFCs, with the highest recorded modulus of 4.16 GPa for a uniaxial NFC sample, and 3.41 GPa for a crossply sample. Scanning electron microscopy observations confirmed that the nanofibrillar structure and excellent alignment was maintained. Comparisons were also drawn between the composites created in this study, and previous work on microfibrillar composites.