We report the spatial anisotropy of the acoustooptical figure of merit M 2 in LiNbO 3 :MgO and GaP crystals. The analysis is based on the indicative surfaces being calculated for different geometries of the acoustooptical diffraction. Basing on these results the most efficient geometries of the acoustooptical cells made of these crystals are determined. It give a possibility to increase the application efficiency of LiNbO 3 :MgO and GaP crystals as sensitive elements for acoustooptical high-frequency control of powerful laser irradiation.