A keyboard includes a base plate, key switches and a backlight module. The base plate has posts. The backlight module includes a masking plate, a light guiding plate, a light emitting unit, a reflective plate and an attaching layer. A plurality of upper through holes are formed on the masking plate. An upper attached area is defined by a periphery of each of the upper through holes. A plurality of penetrating holes are formed on the light guiding plate. A plurality of lower through holes are formed on the reflective plate. A lower attached area is defined by a periphery of each of the lower through holes. The attaching layer attaches the lower attached area with the upper attached area. The lower attached area is attached to the upper attached area via the corresponding penetrating hole, so as to block side walls of the corresponding penetrating hole.