The structural properties of binary alloy compounds of the ZnO-MgO system have been investigated. Pulsed laser deposition (PLD) yielded single-phase films of wurtzite-type (Zn1-xMgx)O within the compositional range of x <= 0.47. After annealing, the (Zn1-xMgx)O films with x >= 0.18 decomposed into a rocksalt-type and a wurtzite-type phase, whereas the sample with x = 0.12 remained as wurtzite-type single phase. Thus, the solubility limit of this system seems to be within the range of 0.12 < x < 0.18. However, the lattice constants of the alloy film with x < 0.12 varied with annealing temperature. These behaviors indicated the highly non-equilibrium nature of (Zn,Mg)O alloy film grown by PLD. (c) 2005 Published by Elsevier B.V.