The precipitation of BaSO4 is an in literature thoroughly discussed precipitation reaction. Here the precipitation of BaSO4 by applying a miniemulsion technique is introduced. This technique involves the preparation of two stable water-in-oil submicron sized emulsions (miniemulsions) via high pressure homogenisation. N-decane presents hereby the continuous phase. The dispersed phases are water based BaCl2- and K2SO4-solutions. Each emulsion contains one of the reactants within the water droplets. After blending the two precursor miniemulsions, the mixture is high pressure homogenised again. During high pressure homogenisation droplets coalesce which induces the formation of nanoparticles by precipitation. The high pressure homogenisation process is chosen in order to allow for controlled droplet-droplet coalescence. Parameters influencing droplet coalescence and particle synthesis such as the homogenisation pressure, the dispersed phase fraction and the precursor concentration are presented. (c) 2010 Elsevier B.V. All rights reserved.