Most solar thermal power generation systems use mirrors over a large area to concentrate solar energy onto the absorber tube. The optical properties of the mirrors directly affect the performance of the concentrating system. Corrosion attack was observed on these mirrors exposed to ambient which cause reduction in optical efficiency as well as working life of the mirrors. Stereo micrograph images and Energy-dispersive X-ray spectroscopy (EDS) results of the mirror samples confirmed loss of silver due to corrosion. Accelerated corrosion testing of few unexposed mirror samples confirmed that factors such as moisture permeability and the reaction of silver with chloride ions at the Cu-Ag interface play a key role in the degradation of the thin silver metal coating. Additional polymer coating on back surface of the mirror was found to be effective in resisting corrosion from ozone and UV radiation. This paper presents study of corrosion prevention of the thin silver layer of the mirror by different polymer protective coating given additionally on their back surfaces. To improve the life of mirror the thin metal coatings must have uniform thickness, be contaminant free, properly edge sealed and have protective coating applied on the back surface. © 2012 University of Manchester and the authors.