Provided is a sphere-shaped coated magnesium oxide powder having a surface coated with a double oxide and having an average shape factor of 1.25 or less, wherein the powder is advantageous not only in that it has excellent humidity resistance, but also in that it has excellent filling property and excellent flowability when being used as filler for a resin. In addition, provided is a method for producing a sphere-shaped coated magnesium oxide powder, wherein the method comprises allowing a compound of an element forming a double oxide to be present on the surface of magnesium oxide powder, and then fusing the resultant magnesium oxide powder at a high temperature so that the surface of the magnesium oxide powder is coated with the double oxide and the magnesium oxide powder is shaped into sphere. Further, provided are a resin composition comprising the sphere-shaped coated magnesium oxide powder and an electronic device using the resin composition.