In this work, ultrafine full-vulcanized powdered rubber (EA-UFPR) and β nucleating agent were incorporated into isotactic polypropylene (iPP) in order to investigate the combined effects on its mechanical properties and its heat distortion temperature (HDT). A large improvement of Izod impact strength verified as a synergistic effect had been obtained by introducing small amounts of EA-UFPR (≤ 2 wt %) into β-nucleated iPP. Decreased crystallization kinetics was found with increasing the content of EA-UFPR. More interestingly, the transformations of crystalline morphologies from β-spherulites to bundle-like β-crystals were detected due to a possible suppressed self-assembly of nucleating agent after adding small amounts of EA-UFPR. On one hand, the largely improved Izod impact strength can be attributed to the synergistic effects between EA-UFPR particles and β-crystalline morphology on promoting the plastic deformation of matrix. On the other hand, the unique interconnected structures formed by the bundle-like crystals and dispersed EA-UFPR particles were proposed for the enhancement in toughness and HDT. Our work provides an effective way to improve the toughness and heat distortion temperature of iPP by adding small amounts of EA-UFPR (≤ 2 wt %), which are crucial for the industrial application of iPP. Keywords: mechanical properties, heat distortion temperature, crystallization behaviour, crystalline morphology