Soil mechanical composition in the karst area of rocky desertification,Guizhou Province was studied.Results show that with rocky desertification intensified,the content of clay decreased,and the content of sand increased.In the sol profile (A -B -C),clay (smaller than 0.001 mm)g radually increased with depth,whereas sand(in the ranges of 0.01～0.05mm,0.05～0.25mm and 0.25～1mm)gradually decreased.Within the surface layer (0～20mm),the amount of sand decreased,and the amount of clay increased.The content of clay decreased in west part of the area as well.The correlation between the content of clay and organic matter was significantly positive with the correlation coefficient being 0.95.On the contrary,the correlation between sand and organic matter was significantly negative with the correlation coefficient being 0.63.