A frame structure of a backlight module includes a body and a mold frame. A side wall surrounds a bearing surface of the body, and the side wall has at least one stopper and at least one positioning hole. A side edge of the mold frame has at least one positioning post. When the mold frame is disposed on the side wall, the side edge of the mold frame leans against the stopper, and the positioning post of the mold frame is embedded in the positioning hole.