Zn1-xCoxO (x = 0.05, 0.1, 0.15) films were deposited on Si (100) and quartz glass substrates using inductively coupled plasma enhanced physical vapor deposition system with magnetic confinement. Structural and chemical composition characterizations by X-ray absorption spectroscopy and Rutherford backscattering spectroscopy indicate that Co2+ substitute for Zn2+ in the tetrahedral configuration and form homogeneous films with wurtzite structure when x <= 0.15. UV-vis transmittance spectra are used to characterize the optical properties. It is found that both transmittance and band gap of Zn1-xCoxO films decrease with increasing Co content, owing to the enhancement of sp-d exchange interactions and typical d-d transitions. Magnetic measurements show that all the as-grown films exhibit intrinsic ferromagnetism above room temperature. (c) 2006 Elsevier B.V. All rights reserved.