This research aims to evaluate the main chemical and mineralogical characteristics of some deterioration products formed on the stone reliefs of Edfu and Kom Ombo temples, Upper Egypt. It is well known that characterizing the deterioration products and their possible origin helps in determining the most appropriate materials and methods for conservation.Optical microscope, polarizing light microscope and scanning electron microscope equipped by EDX unit (SEM-EDX) were used to characterize the stone and the formed deterioration products from the mentioned temples. The results confirmed that the sandstone grains are of small to medium sized rounded quartz. A notable percentage of iron oxides, which works as a cementing material for the secondary pores of stone, was also detected. X-ray diffraction analysis of the formed deterioration products on the sandstone reliefs of Edfu temple showed the presence of halite (sodium chloride, NaCl) and niter (potassium nitrate, KNO₃) salts. While the formation of some phosphate-based minerals was reported on the reliefs of Kom Ombo temple together with a notable stone surface pigmentation. The formation mechanisms of the mentioned products were proposed and discussed.