Morphology, isothermal crystallization kinetics and melting behaviors of PET modified by low molecular weight of ionomers with different structures, ethylene-sodium acrylate (AClyn) and styrene-sodium acrylate (SAA-Na), have been investigated by scanning electron microscopy (SEM), differential scanning calorimeter (DSC) and polarizing optical microscopy (POM). At both high and low temperature regions, AClyn and SAA-Na act as heterogeneous nucleating agent to induce the formation of PET nuclei. The presence of benzene side group in SAA-Na increased the interactions between PET and SAA-Na, leading better compatibility of PET/SAA-Na than that of PET/AClyn. Although SAA-Na had less sodium ions than AClyn at the same content, SAA-Na exhibited similar efficiency to enhance the crystallization rate of PET with AClyn. Isothermal kinetic analysis showed that the same growth dimension was obtained for PET/ionomers regardless of the structural difference between AClyn and SAA-Na. After isothermal melt-crystallization, the second peak of multiple melting endotherms of PET/SAA-Na had almost the same value with PET/AClyn. (C) 2008 Elsevier Ltd. All rights reserved.