Abstract: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.