Abstarct: Abstract The increase in the production of waste and leachate caused by it, is one of the main characteristics of the current urbanization which is considered one of the most important components affecting the environment. The issue of landfill centers, which due to the lack of proper management, has become a major environmental challenge in the surrounding areas, in addition to many environmental damages, can be affected by various factors by infiltrating the soil laxyers under the liner, while polluting the soil, and also affecting the underground water. put This issue can endanger people's health in the long term. In the present study, tests such as unconfined compressive strength, CBR, direct shear and static triaxial tests were conducted to evaluate the effects of leachate on the hydromechanical parameters of clay liners in the landfill. The results were obtained that uniaxial unconfined strength (UCS), California bearing ratio, drained cohesion (c') obtained from the direct shear test increased with the increase of the percentage of leachate to the soil up to 10%, and then with a trend decreased downwards. Meanwhile, the permeability number and the angle of internal friction of the drained soil (φ') in the direct shear test with the same pollution conditions showed a downward trend up to 10% and then an upward trend.