The present work reports the preparation of nanostructured thermoplastic elastomeric blends (TPEs and TPVs) based on polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) by a novel processing technique, where well-dispersed nanoscale EPDM particles (similar to 40-100 nm) in the PP matrix were obtained after mixing at 180 A degrees C at 50 s(-1) and subsequent micro-injection molding at high melt shear rate (500-700 s(-1)) at 200 A degrees C. For a precise comparison, conventional microstructured TPEs were also prepared. As a result of nanostructured morphology, significant improvement of various physico-mechanical properties such as tensile strength, modulus, elongation at break, tension set, loss tangent, thermal stability, and crystallinity was achieved for the micro-injection-molded samples. For example, Young's modulus, the temperature corresponding to the maximum rate of degradation (T (max)) and crystallinity were 70 MPa, 404 A degrees C, and 18.0 % in the case of the microstructured TPE, which increased to 130 MPa, 418 A degrees C, and 22.5 %, respectively, for the nanostructured TPE. The improved properties of micro-injection-molded samples were analyzed with the help of fine nanoscale morphology of EPDM domains. The influence of micro-injection molding on structure development was predicted from the viscoelastic droplet breakup mechanism and critical capillary number. The results demonstrate a strong effect of melt shearing on the deformation and breakup of the rubber domains and enhancement of physico-mechanical properties of PP/EPDM TPEs, which have a great interest in the industry. This work provides a promising pathway for the design of new TPEs with high-performance for various applications.