Two types of composites－high density polyethylene/polystyrene (HDPE/PS) with clay, and high density polyethylene grafted with acrylic acid/PS (PEAA/PS) with clay－were prepared via melt compounding. X-ray diffraction (XRD) results revealed that the dispersion of clay in compatibilized blends was better than immiscible blends. Positron annihilation lifetime spectroscopy (PALS) has been utilized to investigate the microstructure of two types of composites. The ortho-positronium (o-Ps) intensity for PEAA/PS was lower than that for HDPE/PS. The results provided evidence that the chain segments with carboxyl group would be easier to intercalate the gallery of silicates.