Polysaccharide nanocrystals have led to the development of multifunctional and sustainable materials, but most are glucose-based carbohydrates derived from valuable natural sources. Here, we present a top-down strategy that enables one, for the first time, to isolate xylose-based hemicellulose nanocrystals from available industrial biowastes. By leveraging the selective oxidation of alkaline periodate, as high as 34 wt % solid yield is accessible. The hemicellulose nanocrystals exhibit platelet-like shapes (10-20 nm thickness, 30-80 nm wide), crystalline features, and superior dispersibility in water. We also showcase their successful interface applications for one-dimensional (1D) carbon nanotube (CNT) nanoinks and two-dimensional (2D) transition-metal dichalcogenide (TMD) nanozymes, which are comparable to the traditional cellulose nanocrystals. The scalable, low-cost, and sustainable hemicellulose nanocrystals can be envisioned to provide an alternative for glucose-based polysaccharide nanocrystals, as well as hold promise for the high-value utilization of biowastes.