If the diameter of the drain materials in soft ground is too small compared to its length, drain materials are deformed due to large consolidation settlement. The objective of this paper is to study on the deformation process of vertical drain materials under consolidation settlement. Here, consolidation test with multiple loading steps was conducted for clayey soil where drain material has been installed vertically. And deformation behavior of the drain material in the soil was investigated using X-ray CT scanner at the end of each consolidation steps. The drain materials used in these tests were paper and PVD (Prefabricated Vertical Drain). PVD is a drain material with plastic core used at the site. In the results, deformation processes of drain material were visualized using X-ray CT and the difference of the deformation for both materials were observed. In case of using paper as a drain material, the paper was not deformed with simple behavior but with its complicated shape. On the other hand, in case of using PVD, it follows consolidation settlement by a firstly formed curve spreading in horizontal direction. Furthermore, the tests revealed that the deformation of drain materials gives an influence on the surrounding soil. According to all the results shown in this paper, it is concluded that the X-ray CT scanning is an effective tools and deformation process of the drain materials in the soil was firstly investigated in the world.