Abstract <p>At present, strontium hexaferrite is one of the promising materials for production of permanent magnets [1–3], electrical and microwave devices [4–5], etc. In this regard, the study of Ca-substituted strontium hexaferrite is of particular interest since calcium is cheaper than strontium and will allow reducing the production cost of the material. However, it is necessary to study the effect of such doping on the hexaferrite structure and properties. Hexaferrite also has prospects as a material for biomedical applications. However, when hexaferrite decomposes in the human body, strontium can partially replace calcium in bones, while excess of strontium and a lack of calcium can, in turn, lead to negative consequences for the human body [6–15]. Therefore, specimens of Ca-substituted strontium hexaferrite have been studied in this work. Specimens composed of Sr<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(_{{1 - x}}\)</EquationSource> <!--NuclPhys2509048Nikolenko-m1--> </InlineEquation>Ca_<i>x</i>Fe₁₂O₁₉ (<i>x</i> = 0, 0.1, 0.2, 0.3, 0.5, 0.75, and 1) have been obtained by the mechanochemical method, followed by annealing at 1200°C. The specimens have been studied employing phase and X-ray diffraction analyses. The curves reflecting change in the lattice periods and the volume of the unit cell <i>V</i> of strontium hexaferrite have been constructed depending on the degree of calcium doping. The miscibility gap of Ca in strontium hexaferrite at 1200°C has been determined. The magnetic properties of the obtained specimens have been investigated. It has been found that calcium doping does not cause a decrease in saturation magnetization. It is concluded that calcium doping can be used to reduce the cost of manufacturing a material and increase its biocompatibility without the risk of reducing its functional properties because of reduced magnetization.</p>