Provided is a method for crystallizing using a laser mask for selectively crystallizing active regions without a laser shot mark, including: providing an array substrate in which N×M active regions are defined; positioning a laser mask having first and second blocks over the substrate, wherein the first and second blocks have first and second mask patterns, respectively, and the second mask pattern is a reverse pattern of the first mask pattern; irradiating a first laser beam onto the active regions through the first block; and irradiating a second laser beam onto the active regions through the second block.