Magnesium oxide (MgO) nanowires have been synthesized by DC arc discharge without using metal catalysts. These MgO nanowires are singlecrystalline, with an axes along the [100] direction. The cross sectional diameter of the nanowires spans the range of 5–150 nm, with the length up to hundreds of micrometers. The growth of MgO nanowires can be considered as a vapor-phase chemical reaction process, in which both defects and oxygen partial pressure play important roles. The photoluminescence (PL) measurement reveals two emission bands centered at 437 and 496 nm, which can be ascribed to various structural defects and nanosize effect of MgO nanowires. This efficient synthesis method has the potential for large-scale preparation of metal oxide nanostructures, using metals with low melting-points as the raw materials.