A photoelectric conversion element and an optical sensor including the same are disclosed. The photoelectric conversion element may include a plurality of lattice stacks repeatedly stacked on top of each other on a substrate and configured to have an effective band gap. The plurality of lattice stacks may each include a first active layer and a second active layer on the first active layer. The first active layer may include a first two-dimensional material having a first band gap. The second active layer may include a second two-dimensional material having a second band gap not overlapping the first band gap. An effective band gap may be adjusted based on the first two-dimensional materials and thicknesses of the first active layer and the second active layer and a number of times of plurality of lattice stacks.