Magnesium oxide (MgO) whiskers (with diameters of about 60-80 nm) formed on the surface of bulk polycrystalline MgB2 superconductor at a relative low temperature (720 degrees C) during in situ sintering process. The reaction between Mg and B powders begins at a temperature below melting point of Mg and maintains till about 750 degrees C. The residual Mg powders evaporate and react with trace oxygen to form MgO vapor as the temperature exceeds the melting temperature of Mg and a low supersaturation is required for the growth of MgO whiskers. The preformed MgB2 and MgO crystals act as substrates and the melted Mg powders on the surface of them serve as catalysts during the growth process of MgO whiskers. The growth process of MgO whiskers is dominated by a self-catalytic vapor-liquid-solid (VLS) mechanism.