A backlight module is used in a lighting keyboard. The backlight module includes a light guiding plate and a masking. The masking is disposed on the light guiding plate. The masking includes a support layer, a cover layer and a reflective layer. The support layer includes a first surface and a second surface opposite to the first surface. The cover layer is disposed on the first surface. The cover layer includes a first opening. The reflective layer is disposed on the second surface and faces the light guiding plate for reflecting light emitted from the light guiding plate, so as to enhance lighting efficiency on the first opening. The reflective layer includes a second opening. A shape and a position of the second opening are respectively corresponding to a shape and a position of the first opening.