The flexible organic-inorganic thin film transistors (OITFTs) were fabricated with the structure of Al/ZnO/PVP/Al on PES (polyether sulfone) flexible substrate. PVP [poly-4-vinylphenol] organic gate insulator was coated on Al/PES film by the spin coating method. ZnO active channel layer was deposited on PVP/Si substrate by using atomic layer deposition (ALD) at various temperatures from 80 ~ 140 °C. The structural and electrical properties of ZnO films were analyzed by X-ray diffraction (XRD) and hall-effect measurement system. The carrier concentration and resistivity of ZnO film deposited at 100 °C were found to be about 1017 and 37.7 Ω·cm, respectively. The field effect mobility (μ) and threshold voltage (V TH) of the prepared OITFT were about 0.01 cm2/V·s and 12 V, respectively. The I on/off switching ratio was about 104.