To provide a magnesium alloy with improved corrosion resistance by surface modification, and a production method thereof. (1) The surface-modified magnesium alloy comprising: a magnesium alloy having an arbitrary shape; a magnesium fluoride layer formed by fluorination of the surface of the magnesium alloy; and a diamond-like carbon layer formed on the magnesium fluoride layer. (2) The method comprising: subjecting a surface of a magnesium alloy having an arbitrary shape to fluorination treatment to form a magnesium fluoride layer on the surface of the magnesium alloy, and then subjecting the magnesium alloy with the magnesium fluoride layer to be placed in a high-frequency plasma CVD device such that a source gas containing carbon is introduced to form a diamond-like carbon layer on the magnesium fluoride layer.