The present work deals with the examination and comparison of the dissolution of spherical monocrystalline (ideal) ZrO2-, monocrystalline (real) ZrO2- and polycrystalline ZrO2- particles in ZrO2 saturated and unsaturated mold slags. Furthermore the dissolution kinetics of Al2O3- particles in unsaturated casting slags were investigated too. The tests were carried out in three different mold slags for the continuous casting of construction steel. The dissolution experiments were realized with a high temperature laser scanning confocal microscope (HT- LSCM) at the temperature of 1550° C. For this purpose the respective mold powder was heated in a platinum crucible within the HT- LSCM to this temperature. Then the particles were dropped into the crucible with the molten casting powder. The dissolution process was observed and evaluated through video and picture processing. The experimental results showed that the dissolution rate in the unsaturated casting slags largely depends on the viscosity of the slag. The dissolution of the various ZrO2 particles and the Al2O3 particles takes longer with increasing viscosity. An erosion of the particles was not observed in any experiment with unsaturated casting slags. The real monocrystalline zirconia particles needed the longest time for complete dissolution in the respective slags. The dissolution of polycrystalline zirconia particles was the fastest. The dominant dissolution mechanism of all zirconia particles was the mass transport in the diffusion boundary layer. In the saturated slags a dissolution process could not be observed for any particle. Only the polycrystalline particles displayed a marginal erosion process in the slag with the lowest viscosity. The Al2O3 particles dissolved much faster in the various mold slags than the ZrO2- particles. The predominant dissolution mechanism was again the mass transport in the diffusion boundary layer. For one of the mold slags it is also possible that the dissolution process is controlled through a chemical reaction at the boundary layer.