Bio active glass of composition 41CaO–44SiO2–4P2O5–8Fe2O3–3Na2O has been heat treated in the temperature (TA) range of 750–1150 °C for time periods (tA) ranging from 1h to 3h to yield magnetic bio active glass ceramics (MBCs). X-ray diffraction studies indicate the presence of bone mineral (hydroxyapatite and wollastonite) and magnetic (magnetite and α-hematite) phases in nanocrystalline form in the MBCs. Electron paramagnetic resonance (EPR) study was carried out to understand the variation in saturation magnetization and coercivity of the MBCs with TA and tA. These studies reveal the nature and amount of iron ions present in the MBCs and their interaction in the glassy oxide matrix as a function of annealing parameters.The deterioration in the magnetic properties of the glass heat treated above1050 °C is attributed to the crystallization of the non-magnetic α-hematite phase.These results are expected to be useful in the application of these MBCs as thermoseeds in hyperthermia treatment of cancer.