Electrochemical luminescence (ECL) under anodic polarization involves an excitation process that is analogous to the excitation process of inorganic electroluminescence (EL) devices, i.e., the so-called impact excitation process. ECL is suitable for facilitating the exploration of new materials to be used for fabricating EL devices, because the luminescent property associated with ECL can be examined by simple electrochemical measurements without fabricating an emitting device. In the present study, MgIn2O4 (MgGaxIn2-xO4) doped with various amounts of Ga3+ were synthesized and their ECL property was investigated to develop a new white-emitting EL material. The ECL spectra of the MgGaxIn2-xO4 largely depended on the doped Ga3+ content. The main peak in the emission spectra of a sample with x = 0.1 was a broad one (400-600 nm). With an increase in the Ga3+ content, the MgGaxIn2-xO4 samples with x = 0.2 and 0.3 showed two sharp emissions (in the form of lines) in the green region and these two sharp lines became main luminescence in the sample with x = 0.3. The surface of an electrode showed white-plane emission in the sample with x = 0.3. This change in the luminescent property upon changing the Ga3+ content appears to be caused by the change in the distribution of the Ga3+ ions in the MgGaxIn2-xO4 structure. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.082111jes] All rights reserved.