Novel morphology of isotactic polypropylene (iPP) crystal, which is quite different from that of usual spherulite, has been observed by scanning electron microscope (SEM). The crystals show 'bamboo leaf-like (BL)' shape with alpha-monoclinic high crystallinity. The BL crystals are formed by neither melt nor glass crystallization, but by a complicated annealing process that goes through mesomorphic phase of iPP. Substrates are not essential for the formation of BL crystals, since the BL crystals are formed both on glass surface and free surface as well as in bulk. Along with the annealing process, a possible explanation for the mechanism of the formation of the BL crystal is proposed. (C) 2003 Elsevier Ltd. All rights reserved.