Abstract: One of the most important design considerations for using geogrids in reinforced soil is their mechanical properties with and without soil codrinement. Therefore, pullout tests, confined tests and direct shear tests were used in this study to investigate the mechanical behavior of geogrids in soil. To use the soil in-situ as the backfill materical is the most economical consideration. Cohesive, weathered mudstone and sandy soil were used in this study for comparison purpose. The results show that the transvend ribs of nexible geogrids tend to twist during pullout. This rotation of the main stress surface causes the pullout resistance of flexible geogrids to be higher than that of stiff ones. The development of confined tensile stress -strain behavior of geogrids can be divided into three stages: pulIout resistance, tensile strength, and failure. The pullout resistance is usually exhausted at strains of 3% or less. Under low confining pressure, pullout resisIance can reach between 20% and 60% of the geogrids tensile strength.While confining pressure is high, pullout resistance reaches about 150% (at the same strain) of tensile strength. The result from direct shear tests indicates that for low confining pressure, the shear plane would pass through the geogrid - mudstone interface; while at high codrining pressure it would pass through the soil mass itself. With fine sandy soil under both low and high confining pressures, the shear failure plane would always pass through the interface of sand and geogrids.