An exemplary backlight module (3) includes a light guide plate (32) and a frame (34) accommodating the light guide plate. The light guide plate includes a main body including two side surfaces (321), and two sliding strips (325). The sliding strips extend outward from the side surfaces of the main body. Each sliding strip includes a flexible detent (326). The frame includes two opposite first walls (341). The first walls defines two sliding guides (3411) slidably receiving the light guide plate whereby the light guide plate is slidable into the frame and detachably fixed in the frame by snapping engagement of the flexible detents with the frame.