Melt-recrystallization in the heating process of poly(butylene naphthalate) (PBN) was studied with X-ray analysis and differential scanning calorimetry (DSC). DSC melting curve of an isothermally crystallized sample showed double endothermic peaks. With increasing the temperature, wide-angle X-ray diffraction (WAXD) patterns of the sample were obtained successively. Crystal structure did not change during the double melting process. The X-ray diffraction intensity decreased gradually in the temperature region up to about 200degreesC, and then increased distinctly before steep decrease due to the final melting. This increase is interpreted as a proof of recrystallization. The temperature derivative curve of the diffraction intensity was similar to the DSC melting curve. (C) 2002 Elsevier Science B.V. All rights reserved.