Torsion-torque-sensing-based load-side acceleration control is proposed for a two-inertia resonance system in this paper. This control uses a torsion torque sensor installed in a reduction gear, and consists of a torsion torque controller and load-side disturbance observer (DOb). In the load side of the gear, the proposed control structure is equivalent to a conventional DOb-based acceleration controller on the motor side. Therefore, because the proposed controller suppresses resonance vibration in an acceleration dimension, torsion-torque-sensing-based load-side acceleration control has the capability of controlling the load-side acceleration. The problem of the conventional acceleration controller and the effectiveness of the proposed acceleration controller are verified by theoretical analysis, numerical simulations, and experiments. Robust stability for parameter variation and stable regions of control bandwidth are also analyzed.