An exposure system includes an exposure apparatus, a mask, a test pattern portion and a uniformity measuring part. The exposure apparatus includes a first module and a second module. The first and second modules each emit light and are overlapped in an overlapping area. The mask includes a plurality of transmission portions which are spaced apart from each other. Each of the transmission portions has a width less than a width of the overlapping area. The test pattern portion includes a plurality of test patterns which are patterned by using the light transmitted through the transmission portions of the mask. The uniformity measuring part measures a uniformity of the test patterns.