We present a vibration sensor based on a cantilever made of a single-crystalline lithium niobate (LiNbO3) plate with a bidomain ferroelectric structure. The sensitive element was made of a rectangular bidomain lithium niobate plate fastened as a cantilever in a polycrystalline alumina clamp. We used in the study a home-made piezoelectric shaker, as well as two different voltage measurement setups: a lock-in and an oscilloscope. The sensitivity of the sensor to sinusoidal vibrational excitations was measured in terms of displacement as well as of acceleration amplitude. We have shown a strongly linear behavior of the response with the vibrational displacement amplitude in the entire studied frequency range up to 150 Hz. The sensitivity of the produced sensor varies from minimum values of 20 μV/nm and 7 V/g at a low-frequency excitation of 23 Hz to peak values of 92.5 mV/nm and 2443 V/g at the mechanical resonance of the cantilever at 97.25 Hz. The smallest detectable vibration depended on excitation frequency and varied from 0.1 nm at frequencies above 48 Hz to 100 nm at 7 Hz. The high thermal and chemical stability of lithium niobate, as well as an efficient conversion of mechanical deformations to voltage, makes the bidomain lithium niobate crystals a promising material for highly sensitive applications, including low-frequency vibrational sensors able to withstand harsh environment and high temperature.