A substrate for an organic light-emitting device which can improve the light extraction efficiency of an organic light-emitting device while realizing an intended level of transmittance, a method of fabricating the same, and an organic light-emitting device having the same. Light emitted from the OLED is emitted outward through the substrate. The substrate includes a substrate body and a number of crystallized particles disposed inside the substrate body, the number of crystallized particles forming a pattern inside the substrate body.