Mass production of uniform MgO nanostructures has been achieved by a thermal evaporation method. X-ray diffraction (XRD) analyses show the product is composed of pure single-crystalline MgO. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations show that the MgO branched nanostructures consist of many slim nanowires growing from the thick MgO rods. The as-synthesized nanowires have a length of several tens of microns and a diameter of several tens of nanometers. The preferred growth direction of the nanowires is [001]. Many nanowires are found to have a dendritic structure and temperature grade is thought to be the main cause of the growth of this structure. Zn nanoparticles scattered on the surface of the MgO rods are thought to be the catalyst of the VLS (vapor-liquid-solid) growth of the MgO nanowires. Room-temperature photoluminescence measurements show that the synthesized MgO nanostructures have a strong emission band at 401 nm and a weak emission band at 502 nm.