In recent years, there has been increasing demand to miniaturize wiring harness connectors in automobiles due to the increasing volume of electronic equipment and the reduction of the installation space allocated for the electronic equipment in automobiles for the comfort of the passengers. With this demand, contact failure caused by the fretting corrosion seems to become a serious problem in the future.In our previous study, 2-dimensional observations of tin plated fretting contacts using SEM (Scanning Electron Microscope) and TEM (Transmission Electron Microscopy) methods were made by changing the tin plating thickness as a parameter. However, these conclusions were made only for the cross-sectional observations. Recently, SEM combined with FIB (Focused Ion Beam) has been developed, but there are few reports about the observations of tin plated fretting contacts. In this report, 3-dimensional SEM observations of tin plated fretting contacts using FIB -SEM method have been conducted. Spatial distributions of tin, tin oxide and so on have been confirmed quantitatively in two plating thicknesses of 1 and 5 m.