Crystallization from the glass of poly(butylene terephthalate) (PBT) has been investigated by small-angle X-ray scattering and differential scanning calorimetry. When PBT crystallizes from the glassy state, the nodule crystalline structures ill nanometer scale forms and the micrometer order objects, i.e., spherulites, are not observed. The nodule size grows and Saturates at a given annealing temperature and increases with increasing annealing temperature. Two temperatures are obtained by the linear extrapolation of the temperature dependence of the reciprocal nodule Size to naught. The equilibrium melting temperatures by the Gibbs-Thomson plot, i.e., the melting temperature versus reciprocal nodule size, ire also the same temperatures. The lower extrapolated temperature corresponds to the equilibrium melting temperature of the alpha-form of PBT. The higher extrapolated temperature is discussed oil the basis of the Strobl crystallization model and can be regarded as the equilibrium mesophase-crystal transition temperature.