We report the microwave-assisted synthesis of the cellulose-carbonated hydroxyapatite (CHA) nanocomposites with CHA nanostructures dispersed in the cellulose matrix by using the cellulose solution, CaCl 2 , and NaH 2 PO 4 . The cellulose solution was previously prepared by the dissolution of microcrystalline cellulose in NaOH–urea aqueous solution. The influences of the heating time and cellulose concentration on the products were also investigated. The X-ray powder diffraction (XRD) and Fourier transform infrared spectrometry (FT-IR) results indicated that the obtained products were the cellulose–CHA nanocomposites. The scanning electron microscopy (SEM) micrographs showed the CHA nanostructures were dispersed in the cellulose matrix. The thermal stability of the cellulose–CHA nanocomposites in air was investigated using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). This method is simple, fast, low-cost and suitable for large-scale production of cellulose-based nanocomposites.