Basic acoustic properties of five MgO-doped LiNbO3 rectangular parallelpiped specimens, having X-, Y-, and Z-cut planes, with different MgO dopant concentrations ranging from 0 to 13 mol % are investigated by line-focus-beam acoustic microscopy. The investigation is conducted to characterize the optical-use MgO:LiNbO3 crystals and wafers and to establish large-diameter crystal growth conditions. Leaky-surface-acoustic-wave (LSAW) velocities are measured on each crystalline plane of each specimen as a function of the wave propagation direction and are compared with the measured chemical composition ratios of Mg/Li/Nb, densities, and lattice constants. It is shown that, as the dopant concentrations increase in the experimental composition region, the LSAW velocities increase almost linearly for all the surfaces and all the propagation directions. The LSAW velocities are linearly proportional to the lattice constants, but inversely proportional to the densities. © 1999 American Institute of Physics.