A keypad assembly including a light guide plate, a keypad, and reflective layers is disclosed. The light guide plate includes reflective patterns that are locally formed on the bottom surface of the light guide plate to reflect a part of light going into the light guide plate to the top surface of the light guide plate. The keypad includes a pad that is in the shape of a box whose bottom is opened by sidewalls and surrounds the remaining portions of the light guide plate except for the bottom surface of the light guide plate and at least one key button placed on the top surface of the pad and outputting light reflected from the reflective patterns to their outside. The reflective layers are formed at the sidewalls of the pad facing the sides of the light guide plate to reflect light irradiated from the sides of the light guide plate back to the sides of the light guide plate.