The crystallization process of isotactic polypropylene (iPP) by heating from the prequenched mesomorphic phase has been studied using wide-angle X-ray diffraction, small-angle X-ray scattering, and optical microscopy. Mesomorphic iPP as quenched shows the well-known nodular structure of ca. 100 angstrom. In heating process the nodules grew larger keeping self-similarity, with the mesomorphic phase partially transforming into the crystalline phase inside the nodules. After reaching the isothermal process, the nodules stopped to grow at a certain quasi-equilibrium size depending on the annealing temperature. During the long annealing, the interface among the nodules became obscure, and the nodules in nanometer scale merge into larger structure of pure alpha-phase in micrometer scale. The relation between the quasi-equilibrium nodule size and the annealing temperature leads an extrapolated melting temperature of the mesomorphic phase, which is located above the equilibrium melting temperature of the alpha-crystal.