Calcium carbonate powders are used in many branches of industry. Their properties strongly depend on the particle size and shape, which on the other hand depend on production method and conditions. The gretest amount of fine sized calcium carbonate is produced by mechanical methods, e.g. grinding of lime stone or elutriation of chalk. For special applications calcium carbonate powders can be produced by chemical reactions. One possibility is the precipitation from aqueous solutions. The properties of the products can be considerably highly varied by varying the conditions of preparation. In the presented publication the influence of selected parameters on the modification of calcium carbonate, the particle size and shape and other values concerning their application were investigated. As starting substances were used calcium chloride and ammonium, sodium and potassium carbonate. The precipitations were carried out either in this way, that one solution was placed into the reactor and the second was added, or by simultaneous inflow of both solutions. The processes were carried out continuously or discontinuously. The temperature, the concentration of the solutions and the residence time were varied. For the characterization of the solids the mineralogical, granulometrical and chemical composition and the morphology were mainly determined. In the experiments, in which one solution was added to the other, the temporal course of the pH value was studied mainly. The continuous simultaneous precipitations were carried out at constant pH values in a reactor, which was controlled by computer. It could be established the conditions where mainly vaterite, aragonite or calcite are formed. As fillers in the paper industry especially aragonitic products and products which were formed by precipitation on marble flour were suitable.