Abstract: Viscosities and densities of aqueous solutions of sodium chloride and potassium chloride and their mixtures at different mole fractions were measured at 298.15K from very dilute to saturated or supersaturated concentrations.The newly extended Jones-Dole type equation,being based on existing extended Jones-Dole equation,could satisfactorily represent the experimental viscosities of the systems studied to very high concentrations.With increasing concentration,higher exponential terms of concentration are necessarily added.The values of simple additivity of viscosity for mixed electrolyte solution have been calculated.They are very near to the corresponding experimental viscosities under some moderate concentration. This has been explained that enough water could be used to hydrate the ions,and so the interactions between ions have negligible influence on the viscosities.With the increasing concentration,the calculated values become increasingly lower than the experimental viscosities.It may be assumed that the interactions between ions become stronger and stronger and the real concentration for either of the electrolytes should be higher in the mixture due to each others presence.