Amorphous Li-doped InZnO and ZnSnO (IZO:Li/ZTO:Li) dual-active-layer thin film transistors (TFTs) were fabricated by radio-frequency (RF) magnetron sputtering. The transmittance of the dual-stacked IZO:Li/ZTO:Li thin film was over 85% in the visible range. X-ray diffraction (XRD) result indicated that the thin film was amorphous. The influence of ZTO:Li layer thickness on the electrical characteristics and bias-stress stability of the dual-active-layer TFT was investigated. With the increasing thickness of ZTO:Li thin film, the saturation mobility (mu(SAT)) increased firstly and then decreased, while the threshold voltage (V-TH) shifted to the positive direction. The TFT with the optimized ZTO:Li thickness showed a superior performance with a mu(SAT) of 33.2 cm(2)/Vs, a V-TH of 3.2 V, a sub-threshold swing (SS) of 0.6 V/decade and a current on/off (I-ON/I-OFF) up to 3.2 x 10(8).