Provided are a mask frame assembly in which deformation of a frame may be reduced, and a method of manufacturing an organic light-emitting display apparatus using the mask frame assembly. The mask frame assembly includes a frame of a rectangular shape, the frame including an opening and a lower surface including first grooves extending in a first direction, a plurality of first auxiliary sticks extending in the first direction across the opening, wherein a first end and a second end of each of the first auxiliary sticks are bonded to an upper surface of the frame, a mask on the plurality of first auxiliary sticks, and a plurality of second auxiliary sticks arranged in the first grooves, wherein one end and an opposite end of each of the plurality of second auxiliary sticks are bonded to a bottom surface in each of the first grooves.