We report on, for the first time, high-performance, sub-2 volts TiO2 thin film transistors (TFTs) enabled by ultrathin ZrO2 gate dielectrics. The effect of ZrO2 thickness on TFT performance is systematically studied. It is found that the TFT performances are enhanced with the reduced ZrO2 thickness, benefiting from the increased gate oxide capacitance (Cox). The TiO2 TFTs with an ultrathin ZrO2 dielectric of 5 nm show a high Ion/Ioff of 7.7×107 and a nearly ideal SS of 72 mV under an ultra-low voltage of 2 V. The high-performance, sub-2 volts TiO2 TFTs show great promise for future portable electronic applications.