The silane KH-550 and carboxyled polypropylene (EPP) were used as compatibilizers in this study. The effect of them on crystalline morphology of polypropylene/molecular sieves type 5A (PP/5A) composites was investigated. IR illustrated that 5A interacts with EPP by forming molecule interaction or hydrogen bonds, but interacts with silane by covalent bonds. Polarized optical microscopy (POM) and X-ray diffraction (XRD) revealed that a suitable amount of silane can promote beta-crystal formation in PP, and the average size of spherulites in the PP/5A/silane is smaller than that of PP. EPP interacts with 5A by molecule interaction and cocrystallizes with PP, leading to the crystal morphology of PP/5A/EPP resembles to that of pure PP. Significant difference was detected in the effect of the two compatibilizers, which attributed to the different compatibility mechanisms. (C) 2007 Wiley Periodicals, Inc.