In-situ fibrillation is one of the most promising techniques for producing composite containing nanofibrillar network. Furthermore, it is an easy, cost effective and scalable way to produce nanofiber. In this work, PA6-based in-situ nano-fibrillar composites containing PPS fibrillar domains have been presented. We investigated the effect of interfacial tension and spreading coefficient to produce nanoscale fibers. Production of PPS nanofibrils with diameters less than 60 nm were successfully achieved using a cost-effective, continuous and fast melt compounding and hot stretching process. This nanoscale fiber diameter was attributed to the low interfacial tension and, positive spreading coefficient between PA6 and PPS phases. However, FTIR analysis indicates no chemical interaction between PA6-PPS phases. We have also elucidated the effect of PA6/PPS viscosity ratios on fiber diameter via thorough investigation of various viscosity ratios of PA6 and PPS resins. The result showed that a viscosity ratio of 0.5 was most favourable for reducing PPS domain size. Overall, this study shows the importance of chemical compatibility for the in-situ nanofibrillation technique to develop nanoscale fibers and, reports nanoscale PPS fiber production method which cannot be produced via typical electrospinning technique.