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Optical and electronic properties of Zn1-xMgxO teary alloys of wurtzite structure are calculated by using first-principles based on the framework of generalized gradient approximation to density functional theory with the introduction of the on-site Coulomb interaction.The use of the U parameter on Zn-3d and O-2p orbits is obviously crucial,which can improve the GGA to predict the electronic properties and bandgap of the Zn1-xMgx O (0≤ x ≤0.25) system reasonably.It is further demonstrated that the bandgap widens with an increasing Mg concentration from 3.217eV of ZnO to 3.877eV of Zn0.75Mg0.25O.Therefore,the theoretical results show that Zn1-xMgxO teary alloys are potential candidates for optoelectronic materials,especially for UV photon emitters and detectors.In recent years,a great effort has been devoted to research on ZnO,inspired mostly by the fact that wurtzite-structure ZnO is a wide bandgap semiconductor with bandgap energy of 3.37eV and exciton binding energy of 60 meV.[1] Doped ZnO has become a new trend in research and technological applications as its electronic and optical properties can be greatly improved.[2-6] Doping of Mg into ZnO can further widen its bandgap.Both experimental[5] and theoretical[7-10] investigations have shown that the bandgap of Zn1-xMgxO alloys increases with the increasing Mg concentration and the wurtzite structure is stable with x ＜0.33.