A novel inertial sensor based on ferrofluids is presented in this work The proposed device exhibits a widely tunable operating range and high sensitivity.. The ferrofluid is a special solution of magnetic particles in a colloidal suspension whose flow or density and other physical features can be controlled by magnets or magnetic fields. The device prototype is made of one excitation coil and two internal sensing coils, in a differential configuration, wound around a glass pipe where the ferrofluid is contained. The bias magnetic force, induced by the excitation coil, attracts the ferrofluid at the pipe?s centre thus exploiting the role of an equivalent mechanical spring. The force to be measured reflects therefore in the inertial mass amplitudes oscillation that are sensed by using the built-in differential transformer whose output voltage is a function of the ferrofluidic agglomerate position. Analytical models, simulations and experimental results are presented to demonstrate the suitability of the proposed approach.