Superparamagnetic Fe₃O₄ nanoparticles with positive surface 両-potential were synthesized via a solvothermal route. After Fe₃O₄ was mixed with HAuCl₄ and NaBH₄, the reduced Au nanoparticles could be directly adsorbed onto the surface of Fe₃O₄ nanoparticles. The as-synthesized nanocomposites were successfully applied to photothermal destruction of cancer cells.