In this study, bamboo fibers and parenchyma cells were separated by a physical water-medium method. To compare the characteristics of nanofibrils from these two types of cells, lignocellulose nanofibrils (LCNFs) and cellulose nanofibrils (CNFs) were prepared by different processes. Atomic force microscopy analysis revealed that both fibers and parenchyma cells can be separated into individual fibrils after grinding three times. However, LCNFs had a diameter of 20–40 nm, which was larger than that of CNFs (10–20 nm). Additionally, the films prepared from LCNFs had lower tensile strength, but higher hydrophobicity compared with those from CNFs. X-ray diffraction analysis and tensile test of the films showed that the nanofibrils isolated from fibers and parenchyma cells had similar crystallinity and mechanical properties. This study shows a promising application of bamboo parenchyma cells, which are usually discarded as waste in the processing of bamboo products, in the preparation of nanofibers.