The invention discloses a backlight module. The backlight module includes a light guide plate having an incident side; a mounting bracket including a vertical portion and a horizontal portion, wherein the vertical portion is opposite to the incident side, a gap exists between the vertical portion and the incident side, the vertical portion has a plurality of mounting holes, and the mounting holes pass through the vertical portion and the horizontal portion, thereby forming a plurality of grooves on the horizontal portion; a plurality of optical fibers, wherein the optical fibers are respectively disposed in the grooves and the mounting holes, emitting end faces of the optical fibers are attached to the incident side, and the optical fibers are used for guiding the ambient light into the light guide plate; and a plurality of slide assemblies, wherein the slide assemblies are respectively put around the optical fibers and fixed on the optical fibers, and the sliding assemblies are respectively disposed in the grooves and able to move with expansion or contraction of the light guide plate. The invention also discloses a liquid crystal display device having the backlight module.