Atomic force microscopy, reflection high energy electron diffraction (RHEED), and x-ray photoelectron spectroscopy (XPS) have been used to follow the regeneration of atomically flat magnesium oxide (100) surfaces from samples initially etched in phosphoric acid. This regeneration process has been carried out by annealing samples at high temperatures in a range of gas compositions. The gas compositions investigated include argon, nitrogen, carbon dioxide, high partial pressures of water in nitrogen, and a range of partial pressures of oxygen; While acid etching produces initially rough sui-faces, high temperature anneals (1000 degrees C) are found to significantly reduce the surface roughness independent of gas composition. In contrast, only annealing circles in the presence of oxygen (O-2) produced atomically flat stoichiometric MgO surfaces exhibiting good crystalline character, evidenced by distinct square-shaped terraces with well-defined step edges, a 1X1 RHEED pattern, and a 1:1 ratio between magnesium and oxygen determined by XPS analysis.