The objective of this work is to synthesize pure and magnesium-substituted hydroxyapatite (HAp and Mg-HAp) powders with different MgO content in synthesis media (in the wide range of 0.1-10.0 wt% in respect to Ca), and to study the influence of Mg2+ ions substitution on the physicochemical properties of HAp materials. In this work HAp and Mg-HAp were synthesized by modified wet chemical precipitation of homogenous suspension of Mg(OH)2/Ca(OH)2 and H3PO4 solution. Systematic investigation on as-synthesized and sintered HAp and Mg-HAp samples shows that the incorporation of MgO promotes decomposition of HAp to Mg-substituted β-tricalcium phosphate (β-TCP) and significantly modified its microstructure. The effect and evidence of incorporation of Mg2+ ions into HAp structure is discussed.