The electrical properties of Ca10-xMx(PO4)(6-x)(SO4)(x)F-2 apatite structure where M = Na, Li using the complex impedance method allows us to demonstrate the mixed ionic conduction (anionic and cationic). This effect can be assigned to the three-dimensional character of the diffusion process in these materials. The present study proves several factors are responsible for the diffusion processes particularly the cationic site nature, the size and the polarisability of cations introduced in the system.