The method of preparing spherical silica nanoparticles from the oil shale ash (OSA) via the ultrasonic technique in the hydrolysis-condensation stage followed by azeotropic distillation, was reported. The effects of ultrasonic and azeotropic distillation on the particle size and distribution have been investigated. Further, the morphology and properties of the silica particles were examined. The X-ray fluorescence spectroscopy (XRF) and Brunauer Emmett Teller (BET) analysis confirmed that the powders consist of silica nanoparticles with high purity, 99.90% and specific surface area of 697 m(2)/g. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analysis indicate that the silica nanoparticles are amorphous and that the surface of silica nanoparticles is modified by the organics. The transmission electron microscopy (TEM) images of the sample show that good dispersion and uniform silica particles with an average diameter of about 10 nm are prepared. The results obtained in the mentioned method prove that the oil shale ash (OSA) can be used for production of silica nanoparticles. (C) 2008 Elsevier B.V. All rights reserved.