The magnetite/hydroxyapatite (HA) composite that facilitates direct bonding to bones through HA and generation of heat from magnetite exposed to AC magnetic field is considered suitable for hyperthermia therapies of cancer in bones. Porous magnetite/hydroxyapatite (HA) composite was prepared by a hydrothermal treatment of α-tricalcium phosphate (α-TCP) and nano-sized magnetite powder mixture having magnetite concentrations varying between 10 and 50 mass% at 120°C under saturated vapor pressure for 24 h. This composite had micro-sized pores of about 400 μm and submicron-sized pores of about 0.2 μm in size and magnetite particle aggregates were strongly trapped in the cages of rod-shaped HA particles only when the magnetite contents were 30 mass% or less. At magnetite concentrations higher than 30 mass%, the composite cannot hold the particles completely and considered unsuitable for biomedical applications. When magnetite/hydroxyapatite (HA) composites with various magnetite concentrations were exposed to high frequency magnetic field for 10 min, the temperature rise in the composite was a function of magnetite concentration and the temperature rise in 30 mass% was 55°C, which is well above the temperature required for treatment. However generation of higher temperatures, which could be achieved by controlling the magnetic field strength, frequency, and exposure time, may be required because the heat loss due to blood flow, etc., is considered during hyperthermia therapies of cancer in bones.