The Midas monument is an impressive cult facade located to the south of Eskisehir province in Central Anatolia, Turkey. It is formed within Yazilikaya tuffs (white and pink). The tuffs of the Midas monument have deterioration problems. In this study, the depth and characteristics of the weathering zones developed within the white and pink tuffs rue investigated through thin section studies, the x-ray powder diffraction method, methylene blue adsorption tests, major element analyses, and some physical parameters. It is found that feldspar minerals are mechanically fractured due to weathering. The tuffs contain a small amount of clay minerals. The weathering of the tuffs produces weathered zones which are 4.5 cm thick within the white tuff and 2.5 cm thick within the pink tuff.