A backlight module with two translucent faces applicable to operations of scanner is used for scanning of transparent documents. The backlight module has a shell and a light source unit disposed in the shell. The shell has a first translucent portion and a second translucent portion corresponding to each other. The light source unit in the shell can emit light via the first translucent portion and the second translucent portion. When the backlight module is used for scanning of a transparent document and the transparent document is placed outside the first translucent portion, the user can preview the content of the transparent document before scanning via the second translucent portion.