The phase that appeared in the pseudo-binary LiGaO2-ZnO system was investigated by powder X-ray diffraction (XRD), selected area electron diffraction by transmission electron microscopy (TEM-SAD) and Raman spectroscopy, especially focusing on the 0.5(LiGaO2)(1/2) - 0.5ZnO composition. A new quaternary wurtzite-derived Zn2LiGaO4 phase was found in this system. The TEM-SAD indicated that the phase possesses an incommensurately modulated ordering. The optical energy band gap of Zn2LiGaO4 was determined to be similar to 4: 0 eV from its diffuse reflectance and photoluminescence spectra; and it was suggested that the Zn2LiGaO4 was a direct semiconductor. (C) 2011 The Japan Society of Applied Physics