The supermolecular structures of iPP fiber/matrix composites as a function of crystallization temperature were studied by means of optical microscopy. The results show that, even though partial melting of the iPP fibers is in favor of initiating the beta-iPP crystal growth, the interfacial morphology of iPP single-polymer composites induced by its own fiber depends strongly on the crystallization temperature. It was found that transcrystalline structures of negative radial beta(III)-iPP or banded beta(IV)-iPP can be produced within the crystallization temperature range 105-137 degreesC, while transcrystallization zone of pure negative radial alpha(II)-iPP crystals is observed at higher crystallization temperature, e.g. 141 degreesC. On the other hand, the surrounding iPP spherulites grown from the bulk are composed of alpha-iPP in the whole crystallization temperature range. However, the optical character of the spherulites is controlled by the thermal condition. (C) 2004 Elsevier Ltd. All rights reserved.