A deposition mask assembly includes a frame including a first opening portion and a second opening portion spaced apart from each other in a first direction, a first split mask group including a plurality of first split masks arranged on the first opening portion in a second direction crossing the first direction, and a second split mask group including a plurality of second split masks arranged on the second opening portion in the second direction, wherein a boundary between adjacent first split masks in the second direction and a boundary between adjacent second split masks in the second direction are at different positions.