To provide a simple surface treatment method for magnesium alloy having a simple process and capable of solving a problem of environmental pollution.

In this surface treatment method for magnesium alloy, sand holes which exist originally on a surface of a workpiece formed by magnesium alloy injection or pressing are cleaned in addition to the removal of rust, corrosion, and contamination of magnesium alloy. This surface treatment method increases the close adhesion property in following processes (electric plating, electric coating, spray coating), dispenses with chemical conversion treatment and film treatment for the workpiece after the completion of injection sands, and performs processes such as electric plating, electric coating, and spray coating directly to solve the problem of environmental pollution by a known chemical process.