On the basis of the special tensile test results under various loading histories, the rate-dependent behaviors of three polymer geosynthetics due to their viscous properties have been investigated. All the investigated polymer geosynthetics show significant loading rate effects, creep deformation, and stress relaxation. Except for the polyester geogrid showing the combined viscosity, all the investigated polymer geosynthetics exhibit the isotach viscosity. An elasto-viscoplastic constitutive model described in a nonlinear three-component model framework is developed to simulate the rate-dependent behaviors of polymer geosynthetics. The developed constitutive model is verified by comparing its simulated results with the experimental data of polymer geosynthetics presented in this study and those available from the literature. The comparison indicates that the developed model can reasonably interpret the rate-dependent behaviors of polymer geosynthetics under arbitrary loading histories, including the step-changed strain rate loading, creep, and stress relaxation applied during otherwise monotonic loading (ML). POLYM. ENG. SCI., 50:550-560, 2010. (C) 2009 Society of Plastics Engineers