Tiantishan Grottoes,also called the Northern Liang Grottoes,are the oldest Grottoes in China. According to records,the no.9 grotto was created during the Tang Dynasty and its polychrome statue and wall paintings were repainted several times in the following dynasties.To aid preservation and conservation of the polychrome statue and wall paintings,modern scientific techniques were used to analyze the polychrome statue and the wall clay.X-ray diffraction and X-ray fluorescence were used to analyze the pigments,and polarized light microscopy was used to analyze the plant stems and other components mixed in the clay,in order to identify the materials.The analytical results indicate that the polychrome statue and the wall paintings have same clay compositions,consisting of quartz,feldspar (plaqioclase and a small amount of k-feldspar),mica (muscovite,chlorite,illite,clinochlore),calcite and a small amount of gypsum.The plant stems found in the clay are straw.The pigments used are Chinese ink as black;cinnabar,red Lead and iron oxide as red,azurite as blue and calcite with a small amount of gypsum as white.These results provide a basis for future restoration of the Tiantishan Grottoes.