Archaeological sites have to be preserved as the witnesses of the earliest human activities. Determination of deterioration processes of stone monuments in archaeological sites is one of the fundamental phases for their preservation. In this study, deterioration problems of excavated andesites from Aigai and Assos archaeological sites were investigated for the purpose of conservation. Within this intent, visual analysis of the andesite deteriorations was carried out with site surveys in four years intervals and basic physical, petrographic and microstructural properties, mineralogical, elemental and chemical compositions of interior parts and exterior surfaces of the andesites were determined and compared. Visual analyses at the sites show that the progress of andesite deterioration after excavation is insignificant during the four years. The experimental results indicated the slight chemical deterioration of the silica and ferromagnesian minerals and calcium-feldspars through the action of carbon dioxide and water during burial resulted in the formation of clay minerals and calcium carbonate and hematite patinas on the andesite surfaces respectively. Presence of clay minerals promotes physical, chemical and biological deterioration. The experimental results indicated that excavations can be carried out by preventive conservation measures to prevent further andesite deteriorations in open air conditions. As for the preventive conservation measures, the study suggests that the controlled drying of the andesites during excavations has to be supplied, clays on the stone surfaces have to be cleaned but but calcium carbonate layer have to be protected and biocides have to be implemented to prevent the biological formations. Site planning such as drainage to keep the water away from the monuments have to be supplied after their excavations.