Zinc oxide (ZnO) films have been prepared on glass substrate in layer-by-layer mode using an atomic-layer deposition (ALD) technique, and a metal-semiconductor-metal structured photodetector has been fabricated on the ZnO films employing interdigital Au as metal contacts. The photodetector shows a cutoff wavelength at around 390 nm and has an obvious responsivity in the whole UVA spectral range. Because the response of the ZnO photodetector covers the whole UV solar irradiation that can reach the earth, the photodetector promises to be useful in monitoring UV solar irradiation to protect people from harm caused by the solar irradiation. Furthermore, the capability of preparing large-area uniform ZnO films of ALD makes it favorable for possible mass production of this kind of photodetector.