  We report the first-ever experimental observation of backward stimulated
Brillouin scattering (SBS) in thin-film lithium niobate (TFLN) waveguides. The
peak Brillouin gain coefficient of the z-cut LN waveguide with a crystal
rotation angle of 20$^{\circ}$ is as high as 84.9m$^{-1}$W$^{-1}$, facilitated
by surface acoustic waves (SAW) at 8.06GHz.
