Abstract: Understanding the nonisothermal crystallization process of polypropylene (PP) under the presence of fibrous β nucleating agents, is essential to improve the mechanical performance of PP. In this paper, the self-assembling β nucleating agent named TMB-5 was controlled to form point and fiber like morphology, and the effect of fibrous TMB-5 on the nonisothermal crystallization kinetics of polypropylene was studied via comparative research method. The results illustrate that TMB-5 can not only impose PP forming β-form crystals, but also help nucleate PP molecules at high temperature and enhance its crystallization rate. Moreover, unlike the punctate pattern, when fibrous TMB-5 plays the role to control the formation of PP crystals upon cooling, α-form crystal prefers nucleating on the growing front of β-form crystal, which may in turn break the development of initial crystals. As a consequence, the crystallization process is relatively slow, and exhibits an atypical three-stage growth mode when TMB-5 self-assembles into fibrous pattern.