Diffusion coefficients were obtained for two compositions of the system H(2)O-sucrose-KCl at 25 degrees C. These plus published diffusion coefficients of the same system at two other compositions led to the construction of three-dimensional surface diagrams. Using these diagrams, the diffusion coefficients of the ternary system were compared with those of binary systems of components. The main diffusion coeffieient of KCl was estimated from the conductivity data of KCl in aqueous solution of sucrose, and the agreement of these with experimental values was found to be satisfactory. The possible cause for the appreciable size of the cross-term diffusion coefficients is discussed.