The miscibility and melting behavior of binary crystalline blends of poly(ethylene terephthalate) (PET)/poly(trimethylene terephthalate) (PTT) have been investigated with differential scanning calorimetry and scanning electron microscope. The blends exhibit a single composition-dependent glass transition temperature (T-g) and the measured T-g fit well with the predicted T-g value by the Fox equation and Gordon-Taylor equation. In addition to that, a single composition-dependent cold crystallization temperature (T-cc) value can be observed and it decreases nearly linearly with the low T-g component, PTT, which can also be taken as a valid supportive evidence for miscibility. The SEM graphs showed complete homogeneity in the fractured surfaces of the quenched PET/PTT blends, which provided morphology evidence of a total miscibility of PET/PTT blend in amorphous state at all compositions. The polymer-polymer interaction parameter, chi(12), calculated from equilibrium melting temperature depression of the PET component was -0.1634, revealing miscibility of PET/PTT blends in the melting state. The melting crystallization temperature (T-mc) of the blends decreased with an increase of the minor component and the 50/50 sample showed the lowest T-mc value, which is also related to its miscible nature in the melting state. (C) 2007 Wiley Periodicals, Inc.