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The microstructure changes of β-nucleated isotactic polypropylene (β-iPP) during the annealing process and the resultant macroscopic physical property responses were comparatively investigated. The results demonstrated that the annealing process not only increased the crystallinity of β-iPP samples but also enhanced the chain-segment mobility in the amorphous region. Interestingly, it was observed that the annealed β-iPP samples obtained at an appropriate annealing temperature exhibited accelerated creep deformation when the tensile creep measurement was carried out at relatively low environmental temperatures and/or small tensile stresses. However, at relatively higher measuring temperatures and/or larger tensile stresses, the role of the crystalline structure in influencing the creep deformation of β-iPP became dominant, and consequently, the creep resistance of β-iPP increased with increasing annealing temperature. Furthermore, it was demonstrated that the creep deformation of β-iPP is also highly dependent on the crystalline morphology.