An easy approach was reported to achieve the simultaneous reinforcement and toughening of polypropylene (PP) via thermally induced self-assembly of β-nucleating agent (TMB-5). The results showed that the processing temperatures dictated the solubility and self-assembly of TMB-5 in the polymer melts to determine the subsequent morphology development of PP. At low processing temperature, TMB-5 did not dissolve into the polymer melt but remained original shape to induce PP to crystallize into spherulites so that it only promoted the formation of β-form crystals to enhance the toughness of the samples. At high processing temperature, TMB-5 gradually dissolved into the polymer melts. On cooling, the dissolved nucleating agent self-assembled into high aspect ratio fibrils through intermolecular hydrogen-bonding interactions. Due to a favorable matching between PP and TMB-5, PP preferred to nucleate and grow orthogonally to the fibril axis and into oriented hybrid shish-kebab morphology with rich β-form crystals. Compared with isotropic spherulites, the anisotropic structure exhibited excellent properties of the β-form crystal and shish-kebab morphology to simultaneously improve the strength and toughness of TMB-5-modified PP samples. With the increasing processing temperature, more dissolved TMB-5 was involved in the self-assembly procedure to generate longer fibrils and induce more lamellae to grow on the surface. As a consequence, the anisotropy of the PP samples increased further, bringing out more improvements of the tensile strength. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40605.