To examine the relationship between time dependent strain and stress behaviors, creep and stress relaxation tests were done for geosynthetic reinforcements. Long-term performance of geogrid is dependent on the viscoelastic behaviors for longtime period. Viscoelastic properties are mainly influenced by not only creep deformation behaviors at the constant confining load and temperature but also stress re-laxation behaviors at the constant strain and temperature. In this study, elastic and viscose mechanical model was suggested and ap-plied to examine the viscoelastic properties of geogrid. Experimental results of creep and stress relaxation tests of geogrid were compared to verify the applied mechanical model.