An overlay mark is described, wherein the overlay mark is used for checking the alignment accuracy between a lower layer defined by two exposure steps and a lithography process for defining an upper layer, including a part of the lower layer and a photoresist patter. The part of the lower layer includes two first x-directional, two first y-directional bar-like patterns. The first x-directional and first y-directional bar-like patterns are defined by one exposure step to define a first rectangle. The second x-directional and second y-directional bar-like patterns are defined by another exposure to define a second rectangle, wherein the second rectangle is wider than the first rectangle. The photoresist pattern, which is formed by the lithograph process, is disposed over the part of the lower layer and is surrounded by the bar-like patterns.