The present paper deals mainly with the adsorption characteristics of magnesium ion in soil and the effect of exchangeable magnesium on some physical properties of soil.The experimental results Indicate that the effect of anions of magnesium salts on magnesium ion to intrude into soil absorbing complex was in the order of CO₃^2- > SO₄^2- > Cl^-.Accompanied by sodium ion,magnesium ion was more easily adsorbed by calcaxeous soil containing magnesium carbonate than when it exists alone in soil solution with a low saliniiy Sodium ion was more easily adsorbed by soil in NaCl-MgCl₂ solution than in NaCl-CaCl₂ solurion when salinity and SAR were given.