Biorefinery processes using lignocellulosic biomass (LB) are currently in full development to fight overconsumption of fossil resources. However, LB can be difficult to transform, especially using biological processes, due to the highly complex network formed by its constituents (cellulose, hemicelluloses, and ligni n). A pretreatment step is usually required, among which steam explosion has been found to be highly efficient and cost effective. Understanding LB recalcitrance and predict its reactivity are challenges, which require a thorough characterization of pretre ated LB. In our project, three structurally different wood species (oak, poplar, and spruce) were pretreated with steam explosion and analyzed to assess physico chemical parameters using a combination of NMR spectroscopy technics. This poster describes tho se techniques and their complementarity to produce a comprehensive characterization of woody biomass samples. The impact of steam explosion on cellulose supramolecular organization was investigated by 13 C multiCPMAS. An increase of cellulose crystallinity concomitant with an increase of aggregate dimension was observed. Changes in the lignin structure, in relation to the decrease of β O 4 bonds, were evidenced. To supplement these findings, polarization transfer kinetics was studied. The dynamical parameter T 1 ρH was thus determined using the Variable Spin Lock (VSL) sequence. Steam explosion led to the apparition of two populations within the lignocellulosic structure: one with decreasing T 1 ρH values associated with a decrease of the molecular order, i.e. de structuring, and with the density of water molecules in the macromolecular assembly, and the other with increasing T 1 ρ H values meaning increased molecular order due to removing of amorphous cellulose. Furthermore, the porosity distribution of these samples was evaluated by low field T 2 measurements at two different water contents. Overall, we were able to evaluate the decrease in porosity of the samples and the evolution of water accessibility during the steam explosion. NMR spectroscopy is thus an efficient and far reaching analytical technique that allows to investigate and better understand the effect of steam explosion of wood at molecular and morphological levels, two key factors to predict wood reactivity for bioethanol production.