Zn1-xCdxO (x = 0.1, 0.2) thin films with highly (0 0 2)-preferred orientations were deposited on glass and Si(1 1 1) substrates by DC reactive magnetron-sputtering method in the atmospheres with different Ar/O-2 ratios. The properties were investigated by X-ray diffraction, optical absorption spectra. XPS, scanning electron microscopy and atomic force microscopy. When the Ar/O-2 ratios change from 1:4 to 1:1, the full-width at half-maximum of the films deposited on glass substrates of Zn0.9Cd0.1O films decreases (from 0.36degrees) gradually and reaches a minimum value of 0.29degrees at the ratio of 1:1; the band gap (E-g) decreases (from 3.149 eV) gradually and reaches a minimum value of 3.099 eV Lit the same ratio of 1:1. When the Ar/O-2 ratios Continue to increase up to 2:1, the FWHM increases to 0.35degrees; the band gap (E-g) increases to 3.114 eV. The variations for Zn0.8Cd0.2O films are the same as for Zn0.9Cd0.1O films. A mechanism for the influence of Ar/O-2 gas ratios on the band gap of Zn1-xCdxO thin films is proposed. (C) 2004 Elsevier B.V. All rights reserved.