<p>Hydroxyapatite (HA) is the major mineral in hard tissue; however, its low biodegradability, osteoinductivity, and toughness need to be improved for its application as bone substitute material. In the current study, the goal was to use an in situ precipitation method to synthesize carboxymethyl cellulose (CMC)-HA nanocomposite and evaluate the effect of CMC concentration on the crystallinity and structure of the nanocomposite. In addition, incorporation of Mg, as a vital element in biological turnover of the hard tissue, was studied. Our results show that Mg presence decreases the crystallinity of the composite. CMC presence and increase in its concentration also lower the intensity of the XRD peaks in the nanocomposite. Together, our works show that Mg and CMC (at different concentrations) can be used for synthesis of undoped and doped CMC-HA nanocomposite without the use of chemical cross linker, that makes the material suitable for bone and dental tissue engineering application.</p> Graphical abstract <p></p>