Hydrogenated amorphous Si (a-Si:H) films were prepared by plasma enhanced chemical vapor deposition (PECVD) techniques, and the effect of nano-structure on the photoluminescence (PL) phenomena of the films was investigated. The films, which were prepared at R.T., contain both amorphous and crystalline phases of 1 similar to 3 nm size nano-crystallites with {100} orientation preference while the films prepared at 500 degrees C are composed of about 6 nm and 150 nm size crystallites. The former exhibit a strong PL intensity near blue light region, while the latter exhibiting little PL phenomena; also, the optical band gap of the former was calculated at 4.2 eV.