A photomask is provided. The photomask is applied to a photolithography apparatus and includes a substrate with a mask pattern disposed thereon. The mask pattern includes at least one main pattern and a plurality of sub-resolution assistant features (SRAFs). The SRAFs are disposed around the at least one main pattern and separated from each other, wherein a distance between each of the SRAFs and the at least one main pattern is about 3 to 10 times a linewidth of the at least one main pattern. The photomask would result in an improved imaging quality on the wafer.