AbstractOne of the greatest obstacles to the real application of solid-state refrigeration is the huge driving fields. Here, we report a giant barocaloric effect in inorganic NH₄I with reversible entropy changes of $Δ {S}_{{P}_{0}\to P}^{{{\max }}}$ Δ S P 0 → P max ∼71 J K⁻¹ kg⁻¹ around room temperature, associated with a structural phase transition. The phase transition temperature, T_t, varies dramatically with pressure at a rate of dT_t/dP ∼0.79 K MPa⁻¹, which leads to a very small saturation driving pressure of ΔP ∼40 MPa, an extremely large barocaloric strength of $\left|Δ {S}_{{P}_{0}\to P}^{{{\max }}}/Δ P\right|$ Δ S P 0 → P max / Δ P ∼1.78 J K⁻¹ kg⁻¹ MPa⁻¹, as well as a broad temperature span of ∼41 K under 80 MPa. Comprehensive characterizations of the crystal structures and atomic dynamics by neutron scattering reveal that a strong reorientation-vibration coupling is responsible for the large pressure sensitivity of T_t. This work is expected to advance the practical application of barocaloric refrigeration.