A mask pattern and a correcting method thereof are provided. The correcting method includes the following steps. An original pattern having a first original contour and a second original contour is provided. The first original contour has a first original corner. The second original contour has a second original corner, which is near the first original corner. The first and second original corners are cut to form a cut pattern. An optical proximity correction (OPC) process is applied to the cut pattern to form the mask pattern.