An isothermal crystallization behavior is observed for poly(propylene) (PP) on the surface of poly(ethylene terephthalate) (PET) fibers. The extensive nucleation on the fiber surface is followed by the development of a transcrystalline phase, while normal PP spherulites appear much later than the transcrystalline phase in regions far from the interface. The crystallization kinetics is followed by spot-intensity measurements at selected areas on the picture frame near the fibers, showing that the kinetics in the transcrystalline zone is quite different from that in the PP bulk. Furthermore, a preferential orientation of the b-axis and/or bc-planes of PP crystallites along the c-axis of PET fibers is found, suggesting that the crystal structure of the fiber material could also influence the development of this phase. © Wiley-VCH Verlag GmbH, 2001.