A mask assembly and a method of fabricating an organic light emitting display device using the same are provided. The mask assembly includes: a mask frame including a window therein; and a mask which is disposed on the window and fixed to the mask frame, wherein the mask includes a plurality of open parts and a plurality of blocked parts which extend in a column direction. Each open part and each blocked part may alternately be arranged in a row direction. Each open part may include a plurality of pixel openings and a plurality of pixel connection openings, which are alternately arranged in the column direction, and a maximum width of the pixel opening may be larger than a maximum width of the pixel connection opening.