A method for fabricating a dual damascene structure includes the following steps. At first, a dielectric layer, a dielectric mask layer and a metal mask layer are sequentially formed on a substrate. A plurality of trench openings is formed in the metal mask layer, and a part of the metal mask layer is exposed in the bottom of each of the trench openings. Subsequently, a plurality of via openings are formed in the dielectric mask layer, and a part of the dielectric mask layer is exposed in a bottom of each of the via openings. Furthermore, the trench openings and the via openings are transferred to the dielectric layer to form a plurality of dual damascene openings.