Transparent conducting In2O3-Zn2In2O5-ZnO thin films with electrical, optical and chemical properties that varied with the composition were prepared by d.c. magnetron sputtering. The maximum carrier concentration and minimum resistivity were obtained for a Zn2In2O5 film prepared on substrates at room temperature (RT) using a target with a Zn content ([Zn]/[Zn + In] atomic ratio) of 0.245, and those of a Zn2In2O5 film prepared at 350 degrees C were obtained with a Zn content of 0.422. A maximum refractive index of about 2.6 and minimum band gap energy of about 3 eV were obtained for the Zn2In2O5 films. A resistivity of 2.9 x 10(-4) Omega cm was obtained in a Zn2In2O5 film deposited at RT. A sheet resistance of 250 Omega/square and an average transmittance above 95% in the visible range were obtained for a Zn2In2O5 film with a thickness of about 20 nm. The etching rate of Zn2In2O5 films was about 500 nm min(-1) when using a 0.2 M HCl solution.