The combined effect of cobalt and iron substitutions in β-Ca3 (PO4 )2 as a potent material for application in hyperthermia and as a bone substitute is presented. Structural analysis reveals the preferential accommodation of Co2+ and Fe3+ at the Ca2+ (5) sites of β-Ca3 (PO4 )2 until the limit of ∼10 mol % and, thereafter, prefer Ca2+ (4) lattice sites. Occupancy of both the Co2+ and Fe3+ ions induces a significant contraction of the β-Ca3 (PO4 )2 unit cell. The Co2+ /Fe3+ co-substitutions in β-Ca3 (PO4 )2 display magnetic characteristics that enhances hyperthermia effect. In addition, the presence of Co2+ in β-Ca3 (PO4 )2 enunciates pronounced antibacterial efficacy against tested microorganisms. Nevertheless, the enhanced level of Co2+ in β-Ca3 (PO4 )2 results to induce significant toxicity. The biocompatibility of the synthesized thermoseeds is verified from the hemolytic tests and cytotoxicity test performed on human sarcoma cell line MG-63. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1317-1328, 2018.