A method for manufacturing a display device includes providing a panel substrate including a panel area, a peripheral area, and a dummy pattern disposed at a boundary between the panel area and the peripheral area. A protection part is disposed on the panel substrate. A first processing line overlaps a first outline of the panel area extending from a first point of an outline of the panel area. A second processing line overlaps a second outline extending from the first point in a direction different from the first outline are defined. The protection part is partially cut along the first processing line. The protection part is fully cut along the second processing line. The dummy pattern overlaps the first point.