Geosynthetics are being widely used as a cost-effective soil reinforcement solution. The use of geogrids to improve soil mechanical behavior has become increasingly common practice in geotechnical engineering applications, as it has unique advantages over other soil improvement techniques due to technical, economical, constructability and sustainability aspects. Mechanical properties of geogrids are of great importance in designing with geogrids. This papers discusses the effect of strain rate of loading on the tensile strength pf polyester (PET) geogrids. This paper presents the results and analysis of laboratory constant strain rate (CSR) tests conducted on polyester (PET) geogrids at strain rates varying from 0.10% to 20% strain per minute. Assessment of variation of geogrid stiffness with time (creep effect) and calibration factor between global to local strains were derived. A proper material characterization of geogrid is essential for numerical finite element modeling. The modeled behavior of reinforced structures is sensitive to the geogrid stiffness rather than the geogrid strength. The higher CSR results in increase of the measured strength and secant modulus. The larger ultimate strength, the higher anticipated secant modulus. The calibration factor CF between global to local strains ranged from 2.08 to 1.99 was measured for the tested polyester geogrid specimens at a stain of 2%. This CF estimation for strain of 2% is in agreement with comparable PET geogrid CF of 2.2, which was introduced by Allen et al. (2002).