A method for fabricating a mask read only memory (ROM) is provided. A plurality of word lines functioning as a gate electrode of a cell transistor and a plurality of first anti-reflective layer patterns are sequentially formed on a semiconductor substrate. An insulator layer is formed over the entire surface of the semiconductor substrate where the plurality of first anti-reflective layer patterns and the plurality of word lines are formed. A spacer is formed at the side walls of the respective word lines by anisotropically etching the insulator layer until the plurality of word lines are exposed. A second anti-reflective layer is formed over the entire surface of the semiconductor substrate where the spacer is formed. A photoresist pattern opening the upper portion of a predetermined region of at least one word line selected among the plurality of word lines of the cell transistor to be programmed is formed on the second anti-reflective layer. An impurity is implanted into a channel region of the opened cell transistor using the photoresist pattern as an ion implantation mask.