A mask assembly includes a frame including first to fourth lateral parts connected to define a frame opening, an open sheet including a body part in which sheet openings arranged in a first direction and a second direction are defined to overlap the frame opening and a connecting part protruding from the body part and at least partially overlapping the frame, and masks, each including a deposition part having deposition openings defined therein and coupling parts that protrude from the deposition part and that are spaced apart from each other with the deposition part therebetween. The connecting part includes a first connecting part and a second connecting part that overlap the frame and a third connecting part and a fourth connecting part that at least partially overlap the frame.