Nanocrystalline delta-Bi2O3 thin films have been successfully prepared by radiofrequency reactive magnetron sputtering on Si(100) substrate using pure Bi as target. The influences of the oxygen flow ratio in the working gas and substrate temperature on the structures and phase components of the thin films were studied. The X-ray diffraction and transmission electron microscope analyses confirmed that the delta-Bi2O3 thin films with high quality are obtained at substrate temperature of about 200 degrees C and oxygen flow ratio between 5% and 10%. The absorption edge of the films has a strong blue shift with increasing the 02 flow ratio due to the quantum confinement effect and it was considered that the indirect allowed transition dominates in the delta-Bi2O3 thin films. The nanocrystalline nature of the delta-Bi2O3 thin films is responsible for the stabilization of high temperature phase in ambient temperature. (c) 2006 Elsevier B.V. All rights reserved.