The wall effect on particle assembling structure in a particle packed bed is an important issue for powder technology. However, the detailed and systematic experimental data about the wall effect on particle assembling structure in a particle packed bed is hardly adequate yet. The distribution of the local void fraction near the container wall in a particle packed bed is measured using X-ray micro computed tomography (CT). The wall of the cylindrical vessel affects the void fraction distribution, and the distribution can be expressed by the damped oscillation function that shows the relation between the distance from the container wall and the local void fraction. The damping factor, the amplitude and two factors in our damped oscillation function varied with the ratio of particle diameter and inner diameter of the cylindrical container. Our empirical equation can be applied for X-ray CT data and also compared with the traditional experimental data by Ridgway and Tarbuck. (c) Koninklijke Brill NV, Leiden and Society of Powder Technology, Japan, 2008.