A new method based on scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) was developed for visualizing the distribution of cesium ions (Cs+) adsorbed by Japanese cedar charcoal. After being soaked in saturated aqueous CsCl solutions, wood charcoal and regular wood samples were embedded in resin, and thin sections of sample were prepared for the Cs+ observations. The Cs+ ions on charcoal could be seen in EDX mapping images and also in line profiles with enough contrast to identify differences between the various carbonized cell wall regions. On the other hand, Cs+ could not be observed in the EDX mapping images of wood samples, despite having been soaked in a saturated aqueous CsCl solution. These results indicate that Cs+ adsorbed on charcoal can be visualized using this method, but not Cs+ in wood. Additionally, oxygen detected on the charcoal by EDX can be regarded as an indicator of the presence of surface functional groups.