A manufacturing method of a casing including the following steps is provided. A magnesium alloy substrate is provided first. Next, a protective film is formed on the magnesium alloy substrate. A grinding treatment, a cutting treatment, or an engraving treatment is then performed to remove portions of the protective film and portions of the magnesium alloy substrate. An electrophoretic coating treatment is performed afterwards to form a light-transmissive coating layer covering the protective film and the magnesium alloy substrate. A casing is also provided.