An electrophoresis cell developed in our laboratory was utilized to determine the zeta potential at the SnO2 (cassiterite)/aqueous Solution (10(-3) mol kg(-1) NaCl) interface over the temperature range from 25 to 260 degrees C. Experimental techniques and methods for the calculation of zeta potential at elevated temperature are described. From the obtained zeta potential data as a function of pH, the isoelectric points (IEPs) of SnO2 were obtained for the first time. From these IEP values, the standard thermodynamic functions were calculated for the protonation-deprotonation equilibrium at the SnO2 Surface, using the I-pK surface complexation model. It was found that the IEP values for SnO2 decrease with increasing temperature, and this behavior is compared to the predicted values by the multisite complexation (MUSIC) model and other semitheoretical treatments, and were found to be in excellent agreement.