Two phase samples containing similar to 70 vol.% Ga2O3 and similar to 30 vol.% yttria-stabilized zirconia (YSZ) were fabricated by sintering powder compacts in air at 1500 degrees C for 1 h and at 1600 degrees C for 1 h and 3 h. Single phase samples of Ga2O3 were fabricated by sintering at 1500 degrees C for 1 h. Sintered samples were packed in Na-beta ''- alumina powder of composition similar to 8.85 wt% Na2O, 0.75 wt% Li2O and 90.4 wt% Al2O3, and were heat treated at 1250 degrees C for up to 20 h. The two phase Ga2O3 + YSZ samples converted into a sodium zirconium gallate of composition Na0.7Ga4.7Zr0.3O8 and balance yttria- stabilized zirconia. The reaction of single phase Ga2O3 was limited to a thin surface layer in which Na-beta ''-gallate formed. Rapid conversion of Ga2O3 + YSZ samples into Na0.7Ga4.7Zr0.3O8 + YSZ occurred by coupled diffusion of O2- ions through YSZ and of Na+ ions through the formed Na0.7Ga4.7Zr0.3O8, similar to the conversion of alpha-Al2O3 + YSZ into Na-beta ''-alumina + YSZ. The phase Na0.7Ga4.7Zr0.3O8 is isostructural with Na0.7Ga4.7Ti0.3O8 which is a one dimensional sodium ion conductor. The conductivity of two phase Na0.7Ga4.7Zr0.3O8 + YSZ composite wasmeasured by Electrochemical Impedance Spectroscopy. (C) 2016 The Electrochemical Society. All rights reserved.