This study reports the production of magnesium oxide (MgO) whiskers on silicon (Si) substrates by the thermal heating of MgB 2 powders. We investigated the structural properties of the as-synthesized whiskers by using X-ray diffraction, transmission electron microscopy, selected area electron diffraction, and scanning electron microscopy. The product consisted of onedimensional whiskers with a square cross-section. The whiskers had a singlecrystalline cubic structure of MgO. The photoluminescence measurement with the Gaussian fitting exhibited visible light emission bands centered at 2.39 eV and 2.91 eV. We proposed the growth of MgO whiskers to follow the vapor-solid mechanism.