The crystallization and melting behaviors as well as the crystalline morphologies of Poly(ethylene terephthalate)/Poly(m-xylylene adipamide) (PET/MXD6) blends have been examined and characterized with the aid of differential scanning calorimetry (DSC) and wide angle x-ray diffraction (WAXD). The isothermal and nonisothermal crystallization behaviors of the blends were studied as functions of the contents of MXD6, catalyst concentrations, and the effects of the interchange reactions between PET and MXD6. Wide angle x-ray scattering has been used to examine the crystalline morphologies of the PET/MXD6 blends, to characterize their crystalline and amorphous phases, and to determine crystallite sizes in the blends. Results indicate that the catalyst has both catalyzing and nucleation effects on the PET/MXD6 blends, with the extents of each effect dependent upon the content of catalyst. In addition the crystalline morphology was found to be dominated by the MXD6 content as well as the crystallization temperature. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2153 2164, 2010