Abstract: The reuse of the sugars from the by-products of the paper and cellulose industries and lignocellulosic biorefineries and facilitating the extraction and the purification of the sugars contained in the hydrolysates of wood. A method for preparing a mixture of monosaccharides and/or of oligosaccharides and/or of polysaccharides via purification of a hydrolysate of lignocellulosic materials, said hydrolysate comprising hemicelluloses in the form of monomers, of oligomers, and optionally of polymers. The method includes at least one step of oxidation of said hydrolysate with at least one oxidant. This method allows a mixture of monosaccharides and/or of oligosaccharides and/or of polysaccharides to be obtained having a reduced quantity of furfural and/or of hydroxymethylfurfural and comprising polymers having a reduced mass molecular in weight and/or in number.