This paper studies surface effects on the mechanical behavior of nanoporous materials under high strains with an improved anisotropic Kelvin model. The stress-strain relations are derived by the theories of Euler-Bernoulli beam and surface elasticity. Meanwhile, the influence of strut(or ligament) size on the mechanical properties of nanoporous materials is discussed, which becomes a key factor with consideration of the residual surface stress and the surface elasticity. The results show that the decrease in the strut diameter and the increase in the residual surface stress or the surface elasticity can both lead to an increase in the carrying capacity of nanoporous materials. Furthermore, mechanical behaviors of anisotropic nanoporous materials in different directions(the rise direction and the transverse direction) are investigated. The results indicate that the surface effects in the transverse direction are more obvious than those in the rise direction for anisotropic nanoporous materials. In addition, the present results can be reduced to the cases of conventional foams as the strut size increases to micron-scale, which confirms validity of the model to a certain extent. This paper studies surface effects on the mechanical behavior of nanoporous materials under high strains with an improved anisotropic Kelvin model. Meanwhile, the influence of strut (or ligament ) size on the mechanical properties of nanoporous materials is discussed, which becomes a key factor with consideration of the residual surface stress and the surface elasticity. The results show that the decrease in the strut diameter and the increase in the residual surface stress or the surface elasticity can both lead to an increase in the carrying capacity of nanoporous materials. The behavior indicating that the surface effects in the transverse direction are more obvious than those in the rise direction for anisotropic nanoporous ma In addition, the present results can be reduced to the cases of conventional foams as the strut size increases to micron-scale, which confirms validity of the model to a certain extent.