Double-modified montmorillonite (MMT) was first prepared by covalent modification of MMT with 3-aminopropyltriethoxysilane and then intercalation modification by tributyl tetradecyl phosphonium ions. The obtained double-modified MMT was melt compounded with polypropylene (PP) to obtain nanocomposites. The dispersion of the double-modified MMT in PP was found to be greatly improved by the addition of PP-graft-maleic anhydride (PP-g-MA) as a "compatibilizer," whose anhydride groups can react with the amino groups on the surface of the double-modified MMT platelets and thus improve the dispersion of MMT in PP. Fourier transform infrared, X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, scanning electron microscopy, and tensile test were used to characterize the structure of the double-modified MMT, morphology, and the thermal and mechanical properties of the nanocomposites. The results show that PP-g-MA promotes the formation of exfoliated/intercalated morphology and obviously increases the thermal properties, tensile strength, and Young's modulus of the PP/double-modified MMT nanocomposites. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 283-291, 2013