We developed nano-fibrillated polyamide 6 (PA6) polyphenylene sulfide (PPS) composites using a co-rotating twin-screw extruder, followed by stretching and isotropization processes. The average diameter of PPS fibrils in the PA6 matrix was in the range of 60-75 nm, as illustrated by scanning electron microscopy (SEM). The influence of the fibrillated PPS on the crystallization kinetics of PA6 was investigated using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The presence of nano-fibrillated PPS significantly increased the crystallization kinetics of PA6. However, the overall crystallinity of the PA6 was slightly decreased with PPS fibrils. Mechanical properties of the nano-fibrillated PA6-PPS composites were also investigated. It was observed that the presence of fibrillated PPS enhanced the tensile properties of PA6-PPS composites as compared with the neat matrix. Overall, this study provides a deeper insight into the fundamental aspects of nano-fibrillation process and presents the basis for the development of nano-fibrillated PA6 composites with controlled morphology to revolutionize the application of PA6 composites.