AbstractFully bleached kraft bamboo pulp (BPFs), fully bleached kraft softwood pulp (SPFs), and bleached cotton linter pulp (CPFs), which have different crystallinities, were oxidized in the TEMPO-NaBr-NaClO system with ultrasonic treatment for producing nanocrystals. The carboxylate content of nanocrystals made from BPFs, SPFs, and CPFs were 2.10, 2.02, and 1.66 mmol/g, respectively. Nanocrystals of BPFs and SPFs had widths of 5 to 15 nm and lengths of 400 to 800 nm. The length and width of CPFs nanocrystals were 200 to 400 nm and 15 to 25 nm. The oxidizing rates of BPFs, SPFs, and CPFs were different. These differences could be attributed to crystallinity. Crystallinity affected microstructures, chemical process, and the efficiency of ultrasonication. Crystallinity also shaped the nanocrystals, since nanocrystals consist of the residual crystalline regions after chemical oxidation and ultrasonication. Fibers of lower crystallinity (such as bamboo) showed a higher reactivity, and the nanocrystals made from low crystallinity materials were longer, thinner, more rapidly formed, and required less energy in their preparation.