The photo detection characteristics of spray pyrolysis deposited ZnO thin film on glass substrate at 250 OC was demonstrated for fabrication of highly stable visible-blind UV photodetector. This photodetector exhibits lower dark current < 0.04 μA, higher UV photosensitivity ∼4750, responsivity of 0.14 A/W and detectivity of 1.24 × 1012 Jones at an average intensity of 140 μW/cm2 of 340 nm. This Ag/ZnO/Ag device show excellent photo response (rise and decay) time of ∼4 and 6 ms with external quantum efficiency of 51%. The observed photocurrent in the device is associated with adsorption and light-induced desorption of oxygen from the defect sites on the film surfaces. The adsorbed oxygen removes the electron trap centers and increasing the free carrier density in ZnO.