The polymorphisms in poly(hexamethylene terephthalate) (PHT), along with their associated melting and spherulite morphologies, were examined by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarized-light microscopy (PLM). The morphology and crystal cells were dependent on the temperature of crystallization. When melt-crystallized at low temperatures (90-135degreesC), PHT showed at least five melting peaks and two re-crystallization peaks upon DSC scanning, and the samples displayed various fractions of both alpha and beta crystals. However, only a single melting peak was obtained in PHT melt-crystallized at 140 degreesC or above, which displayed a single type of beta crystal. In addition, two different forms of spherulites were identified in melt-crystallized PHT, with one being a typical Maltese-cross spherulite containing the alpha crystal, and the other being a dendrite-type packed mainly with the beta crystal. This study provides timely evidence for a critical interpretation of the relationship between multiple melting and polymorphisms (unit cells and spherulites) in polymers, including semi-crystalline polyesters.