In recent years, a shortage of dredged soil landfill is one of the serious issues in coastal construction in Japan. To avoid the issue, applications of dredged soil in geomaterial have been studied. Mixture of Dredged Soil and Steel Slag (MDS) is one of the applications and has the potential to become widely-used geomaterial in future. Because MDS is a composite material, it is important to study on the relationship between the inner structure and the mechanical behavior of MDS for precise estimation of its strength. The authors have been studying on the mechanical behavior of MDS considering inner structure and uniformity of the specimen observed by X-ray CT scanner. This paper will introduce some part of the study.