Macroscopic longitudinal shrinkage in beech or poplar tension wood is higher than in normal wood. This shrinkage is the result of cell walls layers mechanical interactions. In order to complete the basic data with a view to modelling the cell wall, we are interested in shrinkage differences between cell wall layers and especially of G-layer in poplar and beech. Wood samples in green condition are cut with a razor blade, and then dried before observation. SEM observation shows longitudinal shrinkage much more important in gelatinous layer than in other layers. AFM topographic images of same cells, both in water and in air-dry conditions, confirm this result. Measurements on thin sections allow quantitative results around 4.7 % longitudinal shrinkage for G-layer.