Highly photoactive nanocomposites kaolinite/ZnO with various amounts of ZnO nanoparticles (10 wt.%, 30 wt.%, and 50 wt.%) were prepared using simple hydrothermal method. Calcination of the nanocomposites at 600 degrees C led to the kaolinite-metakaolinite phase transformation, to further growth of ZnO crystallites, and to significant increase of photodegradation activity. The nanocomposites were studied using X-ray fluorescence spectroscopy, X-ray powder diffraction, Fourier transform infrared, diffuse reflectance and photoluminiscence spectroscopies, scanning and transmission electron microscopies, BET analysis, and molecular modeling using empirical force field. Photodegradation activity was evaluated by the discoloration of Acid Orange 7 aqueous solution under UV irradiation. Leaching tests confirmed strong interaction between kaolinite matrix and ZnO nanoparticles, and, therefore, high stability of prepared nanocomposites. (C) 2014 Elsevier B.V. All rights reserved.