Some semiconductor particles, such as SnO2 (band gap approximately 3.5 eV), when irradiated with photons of energy greater than the band gap, exhibit changes in electrophoretic mobility. We report experimental data and a second-order kinetic model for the time dependence of photo-induced changes in electrophoretic mobilities of aqueous dispersions of SnO2 particles. All experiments were conducted in the absence of hole and electron scavengers. Comparisons are made between the behaviour, rate constants and quantum yields for surface charge generation found for colloidal SnO2 and those reported previously for TiO2.