A backlight module provided includes a light source, a first light-guided plate, and a second light-guided plate stacked on the first light-guided plate. The first light-guided plate includes a plate body and an extension disposed on an edge of the plate body and extending towards the second light-guided plate aside a lateral side of the second light-guided plate. The plate body and the extension form a seamless light incident surface. The extension has a reflection surface. The reflection surface connects the light incident surface or the surface of the plate body. The light source is disposed at a light incident surface of the first light-guided plate for projecting light into the light-guided plate.