A radio waves guiding window for a metal case is capable of transmitting radio waves smoothly and contains: a metal case. The metal case includes a modification area defined at a position thereof where corresponds to an antenna, wherein a metal material thickness is formed by ceramizating the modification area in a micro-arc oxidation (MAO) process, and a metal material of the modification area is modified to a metal oxide in the micro-arc oxidation (MAO) process. Accordingly, the metal case has brilliant appearance, transmits the radio waves smoothly, and is simplified.