We investigated the ultraviolet (UV) light photostability of nitrogen doped atomic layer deposition (ALD) ZnO:N thin film transistor (TFT). ALD ZnO:N thin films were used as active layers for back-gate TFT devices. The as-fabricated ALD ZnO:N TFT grown at 125 °C shows proper drain current modulation by gate voltage sweep with 5.4 V of threshold voltage and clear pinch-off. However, the threshold voltage was significantly shifted to negative direction by UV exposure due to the increment of carrier concentration, producing the TFT device with no modulation by gate voltage. In addition, we observed the resistivity change of ALD ZnO:N thin films with time after UV exposure. The resistivity decreased by UV light exposure from 1581 to 4.532 Ω cm and then it recovered toward its original value after switching off UV light. Accordingly, the transfer curves of TFT device using ZnO:N active layer were also exhibited recovery characteristics. We adopted a thin Al2O3 passivation layer on the top surface of TFT and observed that the recovery effect was effectively suppressed.