The present invention discloses a key device for a mobile phone, which comprises a printed circuit board (PCB), a key disposed on the PCB and a metal dome disposed above the key. The metal dome is able to make electrical contact with the key. The key comprises a first electrode, a second electrode and a third electrode, and the third electrode is formed as two rings in which the first electrode and the second electrode are disposed respectively. In the key device for a mobile phone provided by the present invention, the key is formed with three electrodes, so when the metal dome makes contact with the first electrode or the second electrode, the three electrodes of the key are electrically connected with each other simultaneously. This imparts the key for a mobile phone with the compatibility, thereby reducing the product cost and shortening the duration of research and development.