A backlight module is adapted to an illuminated keyboard. The backlight module includes a light source assembly and a light guide film. The light guide film has a top surface, a bottom surface, a through hole, a light-incident pattern and a light-exit pattern. The light source assembly includes a light-emitting component configured to emit light toward the through hole. A size of the through hole is smaller than a size of the light-emitting component. The light-incident pattern is located on at least one of the top surface and the bottom surface. The light-exit pattern is located on the bottom surface. A distance from the through hole to the light-exit pattern is greater than a distance from the through hole to the light-incident pattern.