Magnetic fileld was made of Fe₃O₄ particles and soybean licithin which was only 20 nm in diameter. The heat effect was studied under 10 kW, 100 kHz magnetic field. The temperature change was measured by a glass thermometer (±0.1℃) in agarose gel and distilled water with different Fe₃O₄ content respectively. The effect of magnetic intensity was discussed. This was an experimental basis for hyperthermia treatment tumors. The results indicated that the tempereature raised quickly as the increase of Fe₃O₄ concentrations and the magnetic field intensity. The tempereature finally remained constant due to the balance of heat generation and heat transfer to the surroundings. When Fe₃O₄ concentration were 1 g/L and 2 g/L, the balance temperature were respectively 41.9℃ and 47.5℃ as the magnetic field was 2.78×10⁴ A/m. In 1 g/L Fe₃O₄ concentration, the magnetic field intensity were 2.78×10⁴ A/m and 1.11×10⁴ A/m, the temperature plateaus were at 41.9℃ and 30.7℃ respectively. The heat transfer faster in water than in agarose gel.