In this work pure HAp and Mg-substituted hydroxyapatite (Mg-HAp) powders were synthesized by wet chemical precipitation of homogenous starting suspension of Mg(OH)2/Ca(OH)2 and H3PO4 solution. The synthesis of new substituting materials mimicking natural bone still remains interesting objective of the technological research. Hydroxyapatite (HAp) is one of the most used calcium phosphate compounds as bone grafting material in hard tissue implants and as materials for bone-tissue engineering application, due to its excellent biocompability. In considering cationic substitutes, magnesium (Mg) is one of the most important bivalent ions associated with biological apatite. Enamel, dentin and bone contain, respectively, 0.44, 1.23, and 0.72 weight% of Mg. The preparation of synthetic Mg-substituted hydroxyapatite is of great interest for developing of artificial bone substitutes, which are characterised by high bioactivity. According to the literature, the incorporation of Mg in synthetic HAp is limited (between 2.0 and 29.0 weight % of Mg). In this work pure HAp and Mg-substituted hydroxyapatite (Mg-HAp) powders were synthesized by wet chemical precipitation of homogenous starting suspension of Mg(OH)2/Ca(OH)2 and H3PO4 solution. The influence of different amounts of Mg substitution on thermal stability, phase and chemical composition, morphology, and microstructure of synthesized and sintered Mg-HAp powders was evaluated by the following analytical techniques: differential thermal analysis (DTA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR), field emission electron microscopy/energy dispersive X-ray spectroscopy (FE-SEM/EDS).