The crystallization and melting behaviors of the polyesterimide, derived from N,N'-hexane-1,6-diylbis(trimellitimides), 4,4'-dihydroxybenzophenone and p-hydroxybenzoic acid, were investigated by using polarized light microscopy (PLM), differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). The nematic texture of the polyesterimide was observed on raising temperature to 265 degrees C, and the nernatic phase was found to convert to isotropic melt beginning from about 300 degrees C, the ordered nernatic micro-domains still surviving after 320 degrees C. Isothermal crystallization of the samples was performed at 180 degrees C after heating samples at various temperatures in the range of 265-360 degrees C, and a completed crystallization peak can appear on DSC curves up to the heating temperature of 360 degrees C in the presence of the nematic phase and the ordered nematic micro-domains. Non-isothermal crystallization of the samples at different cooling rate was carried out, and the melting of the resulting crystals exhibits double endotherms. It is indicated that a fast crystallization in the nematic phase forms relatively more ordered crystals, which melt at higher temperature, and a slow crystallization in the isotropic phase or in the biphasic melt produces poor crystals, which melt at lower temperature. The crystallized polyesterimide was annealed, which has a minor effect on the high-melting peak but leads to a continual shifting of the low-melting peak to higher temperature with increasing annealing temperature or annealing time. WAXD patterns indicated that the structural transform was not found during annealing process. (c) 2005 Elsevier Ltd. All rights reserved.