Magnesium (Mg) doped hydroxyapatite (HAP)–gelatin (GEL) one-dimensional nanofibers were prepared in the aqueous GEL solution at low temperature (38 °C). The influence of GEL and Mg on morphology and crystal structure was systematically investigated. Different amount Mg doped HAP–GEL and HAP–GEL nanofibrils doped with different amounts of Mg were obtained by self-assembly along with gelatin, and pure HAP and HAP doped with Mg were sphere nanoparticles in the absence of GEL. Fourier transform infrared (FT-IR) analysis showed that chemical bonding between calcium ions of HAP and carboxyl groups of GEL molecules led to a red shift of the 1395 cm⁻¹ band of GEL. The incorporation of Mg ions into the composite phase caused the decrease of the lattice parameters and Ca/P molar ratio in the HAP solid samples. Differential thermal analysis and thermogravimetric analysis (DTA/TG) features and FT-IR spectra of HAPGEL composite materials were very similar to those of dentine.