Polypropylene (PP) is the second most widespread commodity polyolefin. Even a small quantity of inorganic component is sufficient to achieve significant improvement of stiffness, strength, thermal stability, biodegradability, etc. The major drawback of inorgano-organic composite materials is insufficient compatibility of the PP matrix with inorganic filler. A suitable choice of the layered double hydroxide-modifying anion opens a possibility to obtain PP-inorganic nanocomposites without a need to use compatibilizers like maleic anhydride grafted PP. The nanocomposites were prepared by melt blending in a twin-screw mini-extruder and characterized by dynamic mechanical thermal analysis, and electron microscopy. Nonpolar PP matrix mix uniformly with clay organophilized with functionalized surfactant acids, giving rise to composites with improved thermo-mechanical properties. Influences of the anionic modifier and the filler content (2 or 5% w/w) on mechanical properties and nanoscale structure of the composites are discussed. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2429-2438, 2013