A keypad assembly using a waveguide for guiding lights emitted from light emitting devices is disclosed. The keypad assembly includes a switch board having a plurality of dome switches. The keypad also includes a plurality of key buttons; a plurality of light emitting devices included in the switch board; a waveguide formed under the key buttons, the waveguide having a predetermined refractive index to allow lights emitted from the light emitting devices to travel according to an internal total reflection condition; a plurality of reflecting patterns formed in the waveguide to reflect the light traveling through the waveguide toward the key buttons; and an auxiliary layer formed on the surface of the waveguide, the auxiliary layer having lower refractive index than that of the waveguide to make a constant total reflection condition.