[en] The elastic properties of lead-free (Na1/2Bi1/2)TiO3-BaTiO₃ single crystals near the morphotropic phase boundary were investigated by using Brillouin spectroscopy at room temperature. The measured longitudinal elastic constants of unpoled single crystals with a BaTiO3 content of 5% exhibited large changes depending on the scattering geometry, indicating that a substantial acoustic dispersion effect exists in this system. This was attributed to the relaxor nature due to inherent disorder in the A-site of the perovskite structure.