Bioactivity and magnetic properties were investigated in glass and glass ceramics based on the SiO2±Na2O±Fe2O3±CaO±P2O5±B2O3 system to ®nd their suitability as thermoseed for hyperthermia treatment of cancer. The effect of change in compositions on bioactivity was examined in simulated body ¯uids. The glass ceramic samples exhibit Na3CaSi3O8 and Na322XFeXPO4 phases. After dipping the glass ceramic samples in simulated body -uids silica hydrogel ®rst forms, followed by an amorphous calcium phosphate layer. Magnetic and microwave resonance experiments further demonstrate the potential of these glass ceramics for possible use in hyperthermia.