The nano-sized particles of calcium carbonate and barium carbonate have specific characteristics. They are important materials for the industry. The main object of this investigation is to obtain nanoparticles of calcium carbonate and barium carbonate by chemical reaction carried out in microemulsion of water in oil. The nanoparticles obtained are spherical. Their sizes vary from 20 to 30 nm. The shape and size of particles are determinated by electron microscopy. (C) 2004 Elsevier B.V. All rights reserved.