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Buckwheat seeds have a beneficial nutritional profile and are usually used as a whole grain. Thus, they may contribute to an increased intake of dietary fiber. However, comparatively low dietary fiber contents were obtained for dehulled buckwheat seeds. Buckwheat hulls may be added to whole buckwheat flours to influence the nutritional profile. To evaluate the potential of buckwheat hulls as a functional ingredient, their nutritional composition regarding dietary fiber and protein was analyzed. Dietary fiber analysis yielded very high amounts of insoluble fiber (about 90 %) and only minor amounts of other components. The physiological and technological properties of the fiber strongly depend on the structures of the fiber polymers, which were characterized by multiple analytical approaches. Dietary fiber polysaccharides were analyzed by methylation analysis and monosaccharide analysis after acid hydrolysis. Cellulose and xylans were the quantitatively dominating fiber polysaccharides, whereas only minor amounts of pectins were observed. Analysis of the fiber-associated hydroxycinnamates showed only small amounts of <i>para</i>-coumaric acid and ferulic acid. Significant amounts of hydroxyproline were observed in the amino acid profile of the residual protein, which may indicate the presence of structural proteins. Because lignin might also be a quantitatively important part of the fiber, Klason lignin and acetyl bromide soluble lignin were determined. Very high lignin contents of over 25 % were observed for buckwheat hull insoluble fiber. Characterization of the lignin monomers by 2D-NMR and by GC-MS after applying the Derivatization followed by Reductive Cleavage method indicated that guaiacyl units are quantitatively dominating besides smaller amounts of syringyl units. Thus, buckwheat hulls are highly suitable to increase the amount of slowly fermentable insoluble fiber.