A mask assembly includes a mask frame including a cell opening, and an outer frame defined along a periphery of the cell opening, and a cell mask disposed on the mask frame and including a polymer material. The cell mask includes a masking part which includes a deposition part disposed corresponding to the cell opening of the mask frame and including a masking pattern, and a non-deposition part extending from the deposition part, and a bonding part overlapping the outer frame of the mask frame and extending from the masking part. The non-deposition part includes a non-pattern portion, and a pattern portion having a thickness smaller than a thickness of the non-pattern portion.