A mask assembly for thin film deposition and a method of manufacturing the same. The mask assembly includes a glass mask having a first surface and a second surface opposite the first surface, a first metal layer patterned above the first surface of the glass mask, and a second metal layer patterned below the second surface of the glass mask. A plurality of deposition areas are arranged on the glass mask, and a plurality of deposition pattern portions each having a plurality of slits are patterned in the plurality of deposition areas.