Arabinoxylans (AX) are polysaccharides, also considered dietary fibers, found in monocots plants, mainly in cereals. The chemical structure of AX consists basically of a 1,4 linked β-D-xylose backbone with arabinose side chains. Its consumption has been associated to health benefits, such as improvement in glucose metabolism in subjects, immune response in mice and, more recently, its effects on gut microbiota has been reported. For this reason, AX has been studied as a novel class of prebiotics. It is important to highlight that the fine structure of AX directly influences its biological properties. Also belonging to the monocots, Bactris setosa, commonly known as Tucum, is a Brazilian palm plant of the Arecaceae family. Its purple fruit presents a succulent pulp, a fibrous peel, and are consumed by the residents and indigenous population of the Brazilian Cerrado. Few studies were conducted to analyse its health effects, however it has already been demonstrated that tucum has antioxidant properties. Therefore, information about dietary fiber composition in food is fundamental to understand its nutritional and technological aspects. In this sense, the aim of this work was to analyze the chemical structure of AX isolated from tucum soluble and insoluble dietary fibers. For this, tucum was freeze-dried, milled into powder, defatted, and submitted to the AOAC (991.43) method to obtain soluble (SDF) and insoluble dietary fibers (IDF) yielding 22% and 41%, respectively. SDF were submit to Fehling’s solution, giving rise to a soluble (SDF-SF) and insoluble fraction, yielding ±11% and 89% respectively. IDF, subjected to alkali extraction, gave rise to an alkali soluble and insoluble fraction, yielding ± 49% and 46% respectively. SDF-SF fraction and the alkali soluble fraction (KS), were analyzed for its monosaccharide composition, both presented major relative amounts of xylose (59.2% and 90.1%, respectively), followed by arabinose (26.5% and 7.9% respectively) and galactose (8.3% and 2.0% respectively). Uronic acids (4.5 %, glucuronic acid as standard) and fucose (1.5%) were only identified in SDF-SF. Both fractions were also analyzed regarding their glycosidic linkage pattern through methylation analyses. SDF-SF and KS presented the 2,3-Me2-Xyl in greater amounts (37.3% and 79.5% respectively), indicating a backbone of a (1→4) linked β-D-xylan. Also, the main chain of SDF-SF and KS is substituted in O-3 and O-2. The derivatives 2,3,4-Me3-Xyl, 2,3,5-Me3-Ara and 2,3,4,6-Me4-Gal was identified as non-reducing ends in both fractions. The KS fraction presented more derivatives, suggesting a more heterogeneous and branched structure. This is the first report regarding the presence of AX in tucum edible fruits.