This work reports on the direct preparation of Zn1-xMgxO nanoparticles by a solvothermal condition, in which the formation of kinetically stable Mg(OH)(2) was significantly suppressed. The reactions do not need any heat treatment procedures. Structural and spectral analyses indicated that Mg2+ ions were incorporated into the lattice of ZnO with a solid solubility of about 4.25%. With increasing the Mg content, the E-2 mode of ZnO lattice showed a systematic shift towards higher energies, which was explained in terms of an effective mass model.