A method of manufacturing a microlens substrate includes forming a microlens sheet of a photosensitive resin including a lenticular lens array on a lower substrate, exposing the microlens sheet to light through a mask dividing the lenticular lens array into a plurality of portions respectively corresponding to a plurality of cells and defining a boundary between each of the plurality of cells, planarizing a portion of the microlens sheet corresponding to the boundary, and forming a seal line on the planarized boundary to combine the lower substrate with a corresponding upper substrate.