It was ever reported in a communication of this journal that the large crystal grains having "bamboo leaf-like (BL)" morphology were produced by a rapid heating of isotactic polypropylene (iPP) from the mesophase. In order to optimize the condition to generate the BL crystals, heating rate effects on the crystallization behavior from the mesophase of iPP have been studied by utilizing a de-polarized light transmission (DPLT) method. The DPLT sensitively detected not only the cold crystallization from the mesophase around 100-120 degrees C but also the crystal grain growth in a narrow temperature region just below the melting temperature. With increasing the heating rate, both the temperature regions of the cold crystallization and the crystal grain growth shifted toward the higher temperatures. When the heating rate is slow (<20 degrees C/min), the crystal grain growth was not conspicuous. With increasing the heating rate, the rate of the crystal grain growth increased and showed a maximum when the heating rate is approximately 60-80 degrees C/min. However, excessively fast heating (>100 degrees C/min) also suppressed the crystal grain growth. (C) 2012 Elsevier Ltd. All rights reserved.