Geogrids are commonly used as reinforcement materials, and its creep and stress relaxa-tion properties have always been co-existing in the normal service life of many reinforced soil structures. Considering that the strain levels of the reinforcement materials in most reinforced soil structures are gen-erally not more than 2% under the normal working condition, it is particularly important to investigate the long-term properties of geogrids under low loading levels. This study was targeted at the long-term prop-erties of biaxial PP geogrids at small strain. The tests were carried out firstly at room temperature for 1000 hours, followed by tests at higher temperatures under different load levels. The long-term stiffness of the geogrids under small stress / small strain has been obtained from laboratory tests using time temperature superposition. It was found that the long-term stiffness was considerably affected by the stress or strain levels, and that the ones from creep and relaxation tests were different.