An organic light emitting device including a first substrate, a second substrate parallel to the first substrate, and an organic light emitting unit disposed between the first substrate and the second substrate is provided. The first substrate has a plurality of first light guiding microstructures. A distribution density of the first light guiding microstructures is in a range of 100 to 2000 pcs/mm, wherein the first light guiding microstructures are located inside the first substrate and a material of the first substrate includes a photosensitive material.