Cellulose nanofibers (CNF) are nano-sized cellulose fibers with a high aspect ratio, which are produced by fibrillation of pulp. In order to facilitate fibrillation of pulp efficiently, chemical pretreatments are often used before mechanical treatments. We investigated phosphate esterification method as a chemical pretreatment. Using this method and mechanical treatment, CNF could be prepared easily while controlling its size. CNF is known to exhibit low coefficient of linear thermal expansion (CLTE), high modulus of elasticity and high strength because of the extended chain crystals. Further, due to the nano size, the CNF dispersion has extremely high transparency and viscosity. We have developed not only the dispersion of CNF but also the wet powder and the transparent sheet of CNF. As a result, it is expected that CNF can be used in a wide field.