We investigated the electrical properties of ZnGa2O4 via AC (alternating current) Impedance Spectroscopy method comparing with ZnO reference material. Experimentally, AC electrical conductivity of ZnO and ZnGa2O4 were found to be a function of temperature and grain size; i.e., the increase in grain size of the ZnO led a decrease in room temperature conductivity from 1.35 x 10(-7) S cm(-1) to 9.9 x 10(-8) S cm(-1). The temperature dependent resistivity variation of ZnGa2O4 and ZnO were similar to each other with varied responding temperature. Likewise, the conductivity for ZnGa2O4 decrease from 2.2 x 10(-8) S cm(-1) to 3.8 x 10(-9) S cm(-1) upon an increase in grain size from similar to 0.5 mu m to 100 mu m, accordingly. In addition, a rise in temperature caused an increase in conductivity and led to a corresponding shift in the relaxation time towards the lower values. The semicircles in Nyquist plots disappeared at temperature above 250 degrees C and 700 degrees C for ZnO and ZnGa2O4, respectively. The AC measurements were also correlated with the size dependent activation energies (171 meV for 0.5 mu m ZnO and 1200 meV for 0.5 mu m ZnGa2O4). (C) 2014 Elsevier Ltd. All rights reserved.