A mask assembly includes: a mask frame provided with a first opening defined through a center portion thereof and including an outer frame surrounding the first opening and provided with at least one concave portion defined therein; a mask body disposed to correspond to the first opening and provided with second openings defined therethrough and having an area smaller than the first opening; a first sub-mask disposed on the mask body, provided with third openings defined therethrough over an entire area thereof and having an area smaller than each of the second openings, and including a metal material; a second sub-mask disposed on the first sub-mask, provided with fourth openings defined therethrough over an entire area thereof and having an area smaller than each of the third openings in a plane, and including a polymer material; and a welding portion disposed on the second sub-mask in the concave portion.