Cation diffusion through compacted clays is of great interest due to its potential for buffer materials for waste disposal. The importance of the electrokinetic effect on cationic tracer diffusion is investigated by using pore-scale simulations to consider the influence from the electrokinetic properties and topology of clays. It is indicated that the normalized volume charge density has a significant impact on the cationic diffusion. In clays with a large normalized volume charge density, the electrical double layer has the major impact on cationic diffusion. When the ion strength of the pore solution is constant, the flux from the electromigration term can be negligible. However, once an ion strength gradient is added, the electromigration process should be considered carefully due to its non-negligible role to balance the alteration of total flux. The present study could help improve the understanding of the transport mechanism of simple cationic tracers in compacted clays.