Unique magnesia (MgO) nanosheet arrays were fabricated via a promising micro-arc oxidation (MAO) technique on the surface of magnesium alloy. The non-uniform patterning of oxygen evolution on the sample surface and trapping of gas bubbles in the growing film are associated with the formations of the sheet and flower-like structures. These MgO structures may be useful in reinforcing composite materials or in further modifying other nanostructures. (c) 2006 Published by Elsevier B.V.