This present paper deals with the characteristics of phosphate adsorption isotherm of soils and clay minerals.The concentration of phosphate solution was divided into nine levels of which KH₄PO₄.ranged from 15.5 to 310 P per ml,the solutions were prepared and mined with various amounts of KCl solution (as supporting electrolyte) to keep the ionic strength of solution in a constant (0.01M).The ratio of sample weight to solution volume is 1:20 for soil,1:5 for montmorillonite,1:10 for kaolinite and 1:50 for anion ezchange resin.Each sample was shaken for 1 hour and then stood for 24 houre at 35℃.The amount of P adsorbed was calculated from the difference between initial and final concentration of phosphate in solution.