To provide a systematic surface treatment method of magnesium and a magnesium alloy, by which it is possible to impart metallic and bright decorating properties, excellent coating film adhesiveness, high corrosion resistance and functionality to a molded casing and component, made of magnesium or a magnesium alloy.

The surface treatment method of magnesium and a magnesium alloy is characterized by treating a molded magnesium and magnesium alloy product through a combined process indispensably including a combination of four base processes comprising a degreasing treatment, a chemical polishing treatment, a chemical conversion treatment and electrodeposition coating, wherein the compositions of treating solutions are predetermined and/or management conditions and treatment operation conditions are predetermined.