Patina, which is formed on the stone surfaces of historical buildings and monuments as a result of aging, is considered as a value of the building in the conservation of cultural heritage studies. It should be conserved on calcareous stone surfaces whether or not it represents protective characteristics, since it provides information about previous times. Within this respect, the determination of mineralogical composition, and microstructural and chemical characteristics of patina are critical for the conservation decisions. The aim of this study is to determine the characteristics of yellow patina formation on marble and yellow travertine surfaces to constitute a conservation approach in the archaeological sites. In this study, XRD, FT-IR, SEM-EDX, LIBS and TGA were used to determine the characteristics of yellow patina formation on marble and yellow travertine surfaces in Aizanoi, Aphrodisias, Sardes and Hierapolis. Analysis results indicated that yellow patina is mainly composed of calcium oxalate (whewellite or weddelite) minerals. CaO, MgO, Al2O3, SiO2, P2O5, K2O, SO3, FeO and Na2O were observed on the chemical analyses of the same samples. The results of LIBS and SEM-EDX showed that Ca increases, and other elements decrease from surface to the sound inner parts of the stone due to calcium oxalate and gypsum precipitation and clay deposition on the surfaces. The calcium oxalate patina forms a homogeneous film layer on calcite crystals. It is most likely formed by the reaction of calcite and oxalic acid produced by the biological formations on stone surfaces. It is colorless in original. The yellow color may be related with the FeO and clay deposition on the stone surfaces. The outcomes of the study proved the presence of a protective yellow patina formation on yellow travertine surfaces against the weathering effects of water which cannot be distinguished by naked eye. This patina presents same characteristics with the yellow patina on marble surfaces which should be conserved. The results of this study show that the determination of yellow patina is critical to keep irreversible cleaning interventions away from surfaces especially for the monuments that yellow travertine is used as building materials.