This paper reported a novel approach to simultaneous reinforcing and toughening isotactic polypropylene (iPP) by utilizing a commercially available β-nucleating agent TMB. The results showed that processing temperature played an essential role in determining the morphology development of iPP via controlling the solubility and the self-assembly of TMB in the polymer melts. At low processing temperature, TMB didn’t dissolve into the polymer melt but remained its spherical shape, and thus only acted as β-nucleating agent to induce iPP to crystallize into β-form spherulites and enhance the toughness. However, when processed at higher temperature, TMB gradually dissolved into the polymer melt, and self-assembled into fibrous structure with high aspect ratio in the subsequent cooling. Due to a favorable matching between iPP and TMB, the lamellae of iPP preferred to grow orthogonally to the fibril axis and into oriented hybrid shish-kebab morphology with rich β-form crystals. Moreover, with the increasing processing temperature, more dissolved TMB was involved in the self-assembly procedure to generate longer fibrils and induce more lamellae to grow on its surface. As a result, the anisotropy of the PP samples increased further, leading to tremendous enhancement of mechanical properties in TMB modified samples. Compared with the neat PP samples, the tensile strength and impact strength of TMB modified samples increased from 30.1MPa to 40.5MPa and 4.2 kJ/m2 to 9.3 kJ/m2, increased by 34.6% and 116.2%, respectively. Acknowledgements: This work is financiered by National Natural Science Foundation of China (51127003).