We fabricated nanostructured Si/SiO<sub>2</sub> superlattice films for solar cell appliactions. The Si/SiO<sub>2</sub> superlattice films were fabricated by thermal annealing of a-Si/SiO<sub>2</sub> superlattice films. TEM observations revealed the existence of nanocrystalline Si in the Si layer. This sample showed photoluminescence spectrum with peak energy at around 1.5 eV. It was also found that the defect density in the superlattice was reduced by using forming gas annealing. Applying nanosphere lithography and reactive ion etching, we successfully prepared nanostructures on the surface of the superlattice. We also compared the optical properties with the simulation results using rigorous coupled wave analysis.