Provided is a mask assembly including a mask sheet including a pattern part with at least one opening part, and a welding part connected to the pattern part, and a mask frame with the mask sheet mounted thereon and welded to the welding part. The mask sheet includes a first surface configured to fact the mask frame and a second surface opposite to the first surface. The welding part includes a hatching area in which a surface roughness of the second surface is larger than that of the second surface in the pattern part.