A thin type illuminated keyboard includes a light source, a light-guiding frame plate, a keycap, a membrane plate, a switch circuit plate and a base plate. The light source is used for emitting light. The light-guiding frame plate has a concave structure in a bottom surface thereof. The keycap is connected with the light-guiding frame plate and movable upwardly or downwardly with respect to the light-guiding frame plate. The keycap has a light-transmissible character portion. The light source is disposed on the membrane plate and accommodated within the concave structure of the light-guiding frame plate. The keycap, the light-guiding frame plate, the membrane plate, the switch circuit plate and the base plate are sequentially arranged from top to bottom. The light emitted by the light source is guided by the light-guiding frame plate to irradiate the light-transmissible character portion.