Abstract: The derivation of the acoustic wave equation which is valid for piezoelectric semiconductor crystals of any symmetry and for any acoustic propagating direction is presented. Three mechanisms contributing to Brillouin scattering in high resistivity ZnO crystal are analysed. They are the elasto-optic effect, rotational contribution of shear wave and the electro-optic effect induced by the aocompaning potential. Thermal Brillouin scattering in ZnO crystal is performed. All of five independent elastic constants of ZnO crystal in high frequency range at room temperature are measured and the values are smaller than those reported in lower frequency by about 4.5%. Four photoelastio coefficient relations are given and the curve of the reciprocal velocity of quasi-longitudinal acoustic wave in x-z plane 10 depicted.