The aim of this work was to prepare nanocellulose (NC) from beer industrial residuals (BIR) by an acid hydrolysis/ultrasound method using three hydrolysis times (2, 4, and 6 hours). The atomic-force micrographs showed that the obtained NCs had whisker, oval, and spherical shapes. The average diameters of the NCs ranged between 73 and 146 nm. The chemical characterization of BIR and purified cellulose confirmed that α-cellulose content increased from 44 % to 92 % and lignin contents decreased from 32 % to 5 %. FT-IR analysis showed a substantial change in chemical structure of NCs (especially over the 2-hour hydrolysis time) compared to that of purified BIR fibers. XRD results revealed that the NCs' crystallinity and crystallite size were positively affected by acid-hydrolysis time. TGA results showed that the thermal stability of NCs increased as a result of hydrolysis. BIR, a low-value residue, was turned to nanocellulose, a highperformance nanomaterial.