The raw diffraction patterns of the extracted materials were resolved, using the Ruland–Rietveld approach, into their crystalline and amorphous regions based on known cellulose I peaks, and the data of crystallinity listed in Table 1. The results showed that an apparent higher crystallinity was achieved for all NCC samples, in comparison with that of the untreated kraft pulp (49.13%). It was clear that the crystallinity was directly related to its preparation conditions. Amorphous region of cellulose was easy to be approached by sulfuric acid, while the crystalline region was rigid and hard to reach. There was a significant amount of amorphous regions in the kraft pulp, which were disintegrated during the hydrolysis. More amorphous regions removed, samples with higher crystallinity obtained. This was also the reason of the low yield of 25–30%.