A direct type backlight module includes a frame, at least an optical sheet, and at least a light guide source. The frame includes a plurality of peripheral sidewalls, at least one holding portion defined in a top of the sidewalls, and an elastic member defined in the holding portion. The optical sheet having a positioning hole corresponding to the elastic member is fixed in the frame by the elastic member being mounted into the positioning hole thereby pushing an inner surface of the positioning hole towards an outer area of the optical sheet. The light source is disposed under the optical sheet. The optical sheet may be fixed on the frame tightly, and may avoid being deformed effectively due to a stretching force produced by the elastic member.