Proton exchange from the bound to the bulk waters on the oxo-centered rhodium(III) trimer, [Rh₃(μ₃-O)(μ-O₂CCH₃)₆(OH₂)₃]⁺ (abbreviated as Rh₃⁺), was investigated over the temperature range of 219.1–313.9 K using a ¹H NMR line-broadening technique. By solving the modified Bloch equations for a two-site chemical exchange, lifetimes (τ) for proton transfer at pH = 2.7, 3.6, and 7.0 ([Rh₃⁺] = 26 mM, T = 298 K) were determined to be 0.3 (±.08) ms, 2 (±0.3) ms, and 0.2 (±0.2) ms, respectively. From the temperature dependence of the rate, the activation parameters were determined to be ΔH^‡ = 16.2 (±0.5) kJ mol⁻¹ and ΔS^‡ = − 123 (±2) J mol⁻¹ K⁻¹, ΔH^‡ = 14.9 (±0.5) kJ mol⁻¹ and ΔS^‡ = − 141 (±2) J mol⁻¹ K⁻¹, and ΔH^‡ = 45 (±2) kJ mol⁻¹ and ΔS^‡ = − 22 (±5) J mol⁻¹ K⁻¹ for pH = 2.7, 3.6 and 7.0, respectively. All results are reported for a mixed solvent system [acetone : 250 mM NaClO₄(aq) (3 : 1)], which was necessary to depress the freezing point of the solution so that the ¹H NMR signal due to bound water could be observed. The pK_a of Rh₃⁺ was measured to be 8.9 (±0.2) in the mixed solvent, which is near the pK_a for an aqueous solution (8.3 (±0.2)). Surprisingly, the lifetimes for protons on Rh₃⁺ are close to those observed for the Rh(OH₂)₆³⁺ ion, in spite of the considerable difference in structure, Brønsted acidity of the bound waters and average charge on the metal ion.