The fabrication of bioactive hydrophobicized cellulose nanofiber consisted of two steps. First, cellulose nanofiber-apatite nuclei composites were prepared by mixing apatite nuclei with cellulose nanofiber slurry and air-drying. Second, the obtained specimens were immersed in alkylketene dimer. By this final treatment, the surface of cellulose nanofiber-apatite nuclei composites could be hydrophobicized. In order to impart apatite-forming ability to the hydrophobicized cellulose nanofiber, the various amount of apatite nuclei were mixed with cellulose nanofiber slurry, and the bioactivity was evaluated by using simulated body fluid.