Magnetite (Fe3O4) is oxidative resistant and has a half metallic property and is expected to have spintronic applications. In this work, << 110 >>-oriented single crystal magnetite whiskers, 30-300 nm in diameter, were synthesized on a stainless steel plate by means of the combustion flame thermal oxidation process. An electron source with this single magnetite whisker was fabricated by using a microsampling instrument in a focused ion beam system. The spin polarization of the electron source was found to be 15% at room temperature by using a Mott electron polarimeter.