The aim of this thesis is to determine the moisture dependency of elastic and viscoelastic properties and of the hardness of cell walls (S2-layer and middle lamella) of different wood species. In order to obtain a great variability in mechanical characteristics, five different wood species with different microstructural characteristics were investigated: namely spruce, pine, yew, beech and oak. Additionally, one deteriorated wood from the Vasa ship in Stockholm was tested. Nanoindentation tests were realized on latewood cell walls in order to experimentally measure the indentation moduli, hardness and creep properties of wood cell walls. Experiments were performed in humidity conditions of the surrounding environment between 10 and 80% relative humidity. In addition, nanoindentation tests under water using a fluid cell were done. All wood species showed a great moisture dependency in all measured parameters. For example, the indentation modulus for the S2-layer of pine decreases from 20 GPa at 10% RH (around 6% MC) to 2.9 GPa under water (around 30 to 40% MC). In the same moisture range, the creep properties globally increase, while the hardness decreases. In general, yew has the less moisture-sensitive behaviour and the other softwood species the most moisture-sensitive behaviour among the investigated fresh species. The oak sample from the Vasa ship is even more sensitive to moisture than fresh oak. In addition to the experiments, a micromechanical model for the wood cell walls was tested over the same moisture content range as in the experiments. Based on micromechanics in the framework of poromechanics, this model links the layer specific chemical composition and its moisture content with the homogenized material stiffness. Both layers were modeled, the S2-layer and the middle lamella. For comparison of model predictions with experiments, anisotropic indentation theory was applied. The corresponding model allows to describe the relationship between the layer specific chemical components, the moisture content and the indentation modulus. This was used for the S2-layer to predict the influence of the microfibril angle on the indentation modulus. The model showed a moisture-dependency of the stiffness components and of the corresponding indentation modulus. However, for most species, this dependency is underestimated for the ML and overestimated for the S2-layer. Hence, some improvements in the water modeling were implemented in the micromechanical model. This includes the way water is considered in the model as well as different homogenization methods. Also the distribution of water within the cell wall is investigated. Thereby, model predictions could be improved.