Ternary solution isothermal mutual diffusion coefficients (interdiffusion coefficients) have been measured for aqueous mixtures of 0.250 mol-dm−3 sucrose (component 1) with 0.5 and 1.0 mol-dm−3 NaCl or with 0.5 and 1.0 mol-dm−3 KCl (salt = component 2) at 25.00°C using Rayleigh interferometry with computerized data acquisition. Densities were also measured. The volume-fixed diffusion coefficients (Dij)V show the following characteristics. At all compositions (D21)V is much larger than (D12)V and (D21)V is a fairly significant fraction (33 to 68%) of (D11)V. In addition, (D12)V is slightly larger for mixtures containing NaCl than for those containing KCl at the same concentration, whereas (D21)V is significantly larger for mixtures containing KCl. Values of (D11)V are slightly larger for solutions containing KCl than for solutions containing NaCl. The observed trends imply that (D21)V will probably exceed (D11)V in both mixtures if concentrations of NaCl or of KCl are increased much further while maintaining the sucrose concentration at 0.250 mol-dm−3. Finally, the solvent-fixed cross-term diffusion coefficients (D12)0 and (D21)0 are significantly larger than their corresponding (D12)V and D21)V.