This paper presents the production of xylooligosaccharides from autohydrolysis liquors of wheat straw and sunflower stalk, as wells as the antioxidant activity of these autohydrolysis liquors. The autohydrolysis liquors (raw or refined by ultrafiltration) of both wastes were subjected to the action of two different endoxylanase to produce xylooligosaccharides with low degree of polymerization that are potentially useful as food additives. Trichoderma reseei xylanase led to the highest proportion of oligomers with degree of polymerization values in the range 1-3, while Aspergillus niger xylanase gave mainly oligomers with polymerization degree in the range 2-3. T reseei xylanase gave a higher increase in equivalent xylose concentration and produced more monosaccharide than A. niger xylanase. Membranes with a nominal MWCO 1 kDa did not reject antioxidant-related and other low molar mass compounds, and most of these compounds were recovered with monosaccharides in the permeate of the membrane.