Transparent conducting ZnO:Zr thin films were deposited on glass substrates by DC reactive magnetron sputtering in Ar+O2 ambience with different Ar/O2 ratios. The structural, electrical and optical properties of ZnO:Zr films were analyzed by X-ray diffraction, four-point probe measurements and UV–vis spectrophotometers. When Ar/O2 ratio increases from 20:1 to 25:1, the resistivity significantly decreases because of the improvement of the crystallinity. However, with further increase in Ar/O2 ratio, the crystallinity begins to deteriorate resulting in an increase in the resistivity. The films deposited at the optimum Ar/O2 ratio of 25:1 have the minimum resistivity of 1.4×10-3 Ω•cm and a high transmittance of above 92%.