Hydroxyapatite (HAp), Ca₁₀(PO₄)₆(OH)₂, is an inorganic matrix that is the main constituent of bone tissue. Chemically, HAp has similarities with many phosphate salts. Thus, many studies use these salts to develop novel and optimized scaffolds for bone applications. Calcium polyphosphate (CPP) presents the potential for bone replacements due to its biocompatibility and lower toxicity. Nevertheless, to obtain good mechanical properties, it is necessary to associate CPP with polymers, such as alginate. Alginate is a natural polymer, without toxicity, that has been widely used in biomedical applications. Other additives can be introduced in CPP to improve its properties, such as Mg²⁺ ions. These ions participate in mechanisms that are involved in bone calcification and decalcification. In this context, this work presents the development of a composite based on CPP, alginate, and Mg²⁺ ions, as candidates for bone applications. The precipitation of CPP achieved the composites in an aqueous solution, containing pre-solubilized alginate, followed by the addition of Mg²⁺. The materials were characterized by thermogravimetric analysis, scanning electron microscopy, dispersive energy spectroscopy, x-ray diffraction, Raman, and infrared spectroscopy. The results confirmed the formation of composites with different phosphate/alginate ratios, showing a chemical composition with the potential to be evaluated for bone applications.