Increased soil sodicity and salinity through irrigation, ground-water rise or surface runoff alters soil's physical and chemical characteristics and its ability to withstand erosional forces applied by rain and runoff. Experiments were conducted under a rainfall simulator to study how changes in sodium and salt concentration alter the hydraulic conductivity and erodibility of soils. Changes in K were studied in the laboratory, using different sodium adsorption ratio (SAR)/electrolyte concentration (C) solutions. For the sandy loam soil of Toohey forest, K was severely reduced at intermediate SAR and low C values, but K remained high in the Redlands clay soil for all SAR values tested as long as C remained high. Erosion measurements were carried out in the flume of Griffith University's large rainfall simulator, on soils with and without sodium and salt treatments. Sediment loss significantly increased for the sodium-treated soils. Mean aggregate/particle size of the eroded sediment decreased with increased sodicity. Large sodium concentration contributed to the weakening of soil aggregates and their dispersion under the raindrop impact. Electrical conductivity and salt concentration of the runoff decreased exponentially with time during the erosion event. SAR and EC values of the sodium-treated soils also decreased with applied rainfall. The resultant SAR values for soils were similar to those which produced the smallest K values in the laboratory experiment. These results indicate that increased sodicity contributes to increased soil erosion not only through its dispersive action and the reduction in aggregate stability, but also through reduction in the hydraulic conductivity of soils, which in turn increases the surface runoff.