The program FYZCHEM offers quick calculation, extensive graphical representation and comparison of physico-chemical properties of the electrolytes used for electrolytic production of aluminium. Because of the trend to use in practice even more acidic electrolytes, equations describing the physico-chemical properties of acidic bath were selected. The user of the program may obtain quickly useful information on the influence of additives on the particular property. The program uses regression equations, describing variations of particular properties with composition and temperature. Regression equations were constructed on the basis of our own experimental data as well as on the basis of literature data. Some equations were directly adopted from the literature. The program automatically recalculates and displays the composition in both molar % and mass % concentration expressions. By using four graphical windows it is possible to calculate and to compare four arbitrary selected properties among the following ones: temperature of primary crystallization, density, electrical conductivity, viscosity, vapor pressure, alumina solubility, aluminium solubility in the electrolyte, surface tension, interfacial tension Al/melt and density difference Al/electrolyte.