Microparts of isotactic polypropylene (iPP)/polyamide 6 (PA6) blends were prepared with a particular injection molding method known as microinjection molding (MIM). Continuous and strong shear action exerted on the melts of iPP/PA6 directly promoted the formation of in situ PA6 microfibril in MIM. Moreover, hierarchical structures, namely, spherulite, cylindrites, and transcrystallization, were observed in the microparts. The synergetic effect of PA6 in situ microfibrils, beta-nucleating agent (beta-NA), and strong shear action even induced more oriented beta-crystals around the surface of PA6 microfibrils in the core layer and markedly increased the beta-crystal content. Results showed that adding PA6 and beta-NA markedly raised the crystallization temperature of iPP, and the effect of PA6 microfibrils was evidently more pronounced than that of PA6 spherical particles in conventional blends which implies more nucleation sites on the microfibrils. Moreover, strong orientation of iPP molecular chain was also confirmed by 2D-WAXD. It is well worth mentioning that the mechanical property was remarkably improved by these special morphology and crystalline structures.