An edge-lit backlight module includes a back plate, a light bar, and a light guide plate. The back plate has a bottom plate and four lateral sides. Each of the lateral sides is perpendicular to the bottom plate and connected to a peripheral edge of the bottom plate. The light bar is disposed on a side of an internal face of one of the lateral sides to leave at least one accommodation space on the lateral side. The light guide plate has at least one extension portion corresponding to the accommodation space. The light guide plate is disposed on the bottom plate, and each extension portion of the light guide plate engages with the corresponding accommodation space for fixing the light guide plate onto the back plate.