Molecular sieves type 13X (13X) was selected as a filler of polypropylene (PP). The effect of carboxyled polypropylene (EPP) on mechanical properties, melting behavior, morphology and rheology behavior of PP/13X composites was studied. Mechanical properties tests showed that when 4% EPP added, the impact strength and tensile strength increased 65.6 and 4.6% than PP/13X composites, respectively. It was suggested that the EPP activated the heterogeneous nucleation centers on the filler surface, and made 13X dispersed in PP matrix homogeneously by POM. SEM illustrated that EPP improved the adhesion and the compatibility between 13X and PP. Flow tests indicated that the EPP played the role of lubricant in PP/13X. All the investigations showed EPP was a true coupling agent for PP/13X composites. (c) 2007 Wiley Periodicals, Inc.