Using unsuitable material will often result in premature failure of pavement surface and reduction in the ability of pavement to carry the design traffic load.The use of locally natural materials of gypseous soils is necessary to minimize the construction cost. The chemicals and physical tests carried out on this gypsies soil brought from western region of Iraq indicates clayey sand particles with 63% gypsum content. The chemical and physical effects on behavior of gypseous soil is studied by leaching using modifying the standard odometer apparatus to be able for testing a large cell of CBR mold under loading values ( 44.5;178;311 )N with different hydraulic gradient values (2;6;10 ) for sixty days. For this purpose, fifty four CBR samples are prepared at a 95% relative to modified AASHTO compaction. The geotechnical properties of wetting gypseous soils due to the large damages that affect the structures founded and constructed on it. It is observed that the total leaching strain increases, as the surcharge load and hydraulic gradient increase. The results show that the value of CBR increasing with increasing compactive effort (dry density) after leaching gypseous sub grade soil. Decreasing voids particles by compactive effort, cause increase cementing materials which bond the soil particles together and increasing the stiffness. This can has an economic effect in pavement design as this increase in CBR% can transfer unsuitable material into suitable sub-grade gypsum soil.