Abstract: This paper tries to study how the externally applied electric field influence the properties of rock grain and clay minerals, by testing the grain size before and after applying electric current. Electric agglomerating of clay minerals and fine compositions is obviously detected in the electric field, and rock grain size changes too, with the tendency of becoming larger. This tendency is very obvious for small particles, especially for clay minerals. In different areas of the electric field, its effect is different. Specifically, much obvious effect is found at the cathode than that at the anode. The change of grain size is also proportional to the time affected; yet it has no correlation with current strength in the same electric field and the same amount of time.