The authors report on the fabrication of low-driven-voltage and high mobility ZnO thin-film transistor with sputtering Ta2O5 film as the dielectric. The device shows a field effect mobility of 60.4 cm2/V s, a threshold voltage of 1.1 V, an on/off ratio of 1.22×107, and a subthreshold swing of 0.23 V/decade. The high mobility partially resulted from the fringing-electric-field effect due to the undefined active layer. Therefore, considering our device geometry, the actual mobility is about 40.5 cm2/V s. We contribute the high performance to the proper dielectric thickness, smooth insulator surface, and relatively low trap state densities in the insulator/channel interface.