The microstructure is an important factor which affects the engineering properties ofcompacted clayey soil. The microstructures of clayey soils which are remoulded under dif-ferent water contents will change in the process of compaction. As a result, the engineer-ing properties of soils are influenced. In this note, the authors first apply the Videolab image processing system into thequantitative assessment of microstructures of compacted clayey soils. Three quantitative in-dexes are introduced to appraise the orientation of microstructures and the relationships The microstructure is an important factor which affects the engineering properties of compacted clayey soil. The microstructures of clayey soils which are remoulded under dif-ferent water contents will change in the process of compaction. As a result, the engineer-ing properties of soils are influenced . In this note, the authors first apply the Videolab image processing system into thequantitative assessment of microstructures of compacted clayey soils. Three quantitative in-dexes are introduced to appraise the orientation of microstructures and the relationships