[en] The reduction of U(VI) with Sn(II) was studied in 20, 40, 65, and 80 wt percent N-methylacetamide--water solutions. The reaction rates were calculated using the second-order rate equation in 1, 2, 4, and 6 M HCl solutions in all the mixed solvents at 30, 40, and 50⁰C. The change in rate constant with both change in solvent composition and HCl concentration was considered as possibly arising from the composition and charge (including sign) of the reacting complex ions, the macroscopic dielectric constants of the solvents, and the ionic strengths of the solutions. Certain limitations of the NMA-H₂O solvent systems for this reaction and these acidities were pointed out. (U.S.)