The selectivity in transformation of monosaccharides by acido-basic catalysts is a critical point for the development of biomass conversion processes. The objective of this project is to understand at the molecular level the main parameters governing the selectivity of these transformations in Lewis acidic zeolite catalysts. The original approach consist in examining together the different primary reactions of sugars (epimerization, isomerization, retro-aldolisation, dehydration) while considering the differences in reactivity of different sugars from biomass (mainly glucose, xylose and fructose) and several characteristics of the zeolite materials (cation, pore structure...) The study based on two complementary approaches : experimental work including synthesis of materials and kinetic study, and theoretical work consisting in molecular modeling of the possible reaction pathways (DFT).