Zinc-tin oxide (ZTO) films can exhibit high visible light transparency, high electrical conductivity and glass-like dense structures; therefore, they are expected to be applied as transparent conductive oxide and barrier layers. In this study, the influence of the Zn-Sn ratio on the optical properties and microstructures of the ZTO films was investigated. The ZTO films were deposited on glass substrates by reactive magnetron sputtering without intentional substrate heating. The chemical state, crystal structure, density, surface morphology and optical properties were evaluated. The ZTO films deposited using lower Sn concentration targets of 0 to 7 at.% had wurtzite structures of ZnO. In contrast, the ZTO films were amorphous when Sn concentrations of 15 to 100 at.% were used. The ZTO films had higher densities at higher Sn concentrations. Additionally, the ZTO films exhibited smooth surfaces compared with the pure ZnO and SnO2 films. The refractive indices of the ZTO films increased with increasing Sn concentration of the Zn-Sn targets. These results show that the optical properties and microstructures of the ZTO films varied with the Zn-Sn ratio. (C) 2016 Elsevier B.V. All rights reserved.