  We report on the first experimental demonstration of backward stimulated
Brillouin scattering (SBS) in Lithium Niobate on Insulator (LNOI) waveguides.
Performing polarization-dependent pump-probe experiments, we successfully
quantified both intramodal and intermodal scattering among fundamental modes,
showcasing substantial gains up to $G_{B}=$10m$^{-1}$W$^{-1}$. Such large gains
on simple waveguides open a pathway for unlocking novel opto-electro-mechanical
phenomena within the LNOI platform.
