The immiscible polypropylene (PP)/polystyrene (PS) blend was prepared via melt compounding and the preferential intercalation behavior of clay was investigated by wide angle X-ray diffraction (XRD) and transmission electron microscope (TEM). It was found that the clay platelets initially located in the PS phase in PP/PS/Clay composites and PS chains intercalated into the clay layers. However, all clay migrated from the PS phase to the modified PP phase after introducing polar maleic anhydride group (MAH) to PP chains. Interestingly, most of clay migrated from the modified PP phase to the modified PS phase again when PS matrix was modified with sulfonic group, and some enriched in the interphase region. The interaction energy density (B) of the blends was determined by combining the melting point variation with the ternary interaction model for heat of mixing. It was found that the value of B decreased with the introduction of polar group (MAH or sulfonic group), indicating that the polarization of PP and PS can enhance interaction between clay platelet and polymer component. Different interaction between clay platelet and polymer component leads to the preferential intercalation behavior. The higher polarity of the polymer generates higher interaction between clay and polymer component as well as results in stronger preferential intercalating ability. Moreover, the results of FTIR spectra after extraction of all samples gave additional explanation of the preferential intercalation behavior of clay in the immiscible PP/PS blends. On the basis of the results of the measurement mentioned above, a possible mechanism was proposed. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3130-3139, 2008