The optical activity and acoustic properties of La3Ga5SiO14 (LGS) were studied. The optical transmission between parallel polarisers was measured at various wavelengths. Specific rotations were obtained by TU1901 UV-vis spectrophotometer. The experiments indicated that specific rotations of La3Ga5SiO14 were smaller than that of alpha-SiO2. From Christoffel equation the slowness curves on (100), (010) and (001)planes were plotted and acoustic velocities were calculated, showing that the acoustic velocities of LGS crystal were generally smaller than that of alpha-SiO2. Therefore, LGS was a good acousto-optic material. (c) 2005 Elsevier B.V. All rights reserved.