Abstract In this paper, a new method applied to some ionic conductors for measuring fundamental parameters of ionic conduction was developed based on the phenomena of light diffraction produced by a laser beam through these ionic conductors under a low frequency AC field. The ionic conduction parameters of aaaa-LiIO3 single crystal was measured by this method. The results are as follows. The activation energy of mobility Eμ=0.36eV. The formation energy of Frenkel defect EM =0.59 eV. At 300K, both the number densities of positive and negative carriers are 1.6×1017cm-3; their relative concentrations are 1.07×10-5; the effective mobility μeff+=3.9×10-8cm2·s-1·V-1 as the DC field applied to the crystal is antiparallel to its spontaneous polarization (we denote the voltage as V+) the effective mobility μeff- = 3.4 ×10-9cm2·s-1·V-1 as they are parallel (we denote the voltage as V-). Under the action of an AC field, in the half period that is corresponding to V+, it at least need that the ion hops 7 steps to form a space grating, and in another half period ion at least hops 32 steps to cause an oscillating component in the diffraction light intensity.