A transition edge sensor (TES) microcalorimeter detector with an energy resolution of [email protected] mounted on an SEM has been newly developed and applied for the first time to reveal the cellular distribution of Cd in a cadmium hyper-accumulating plant. The elemental maps of the light element P as well as the heavy elements Cd and Zn were also successfully obtained. Similarly, the simultaneous analysis of As L alpha and Mg K alpha in an arsenic-accumulating fern was possible with this system. It is expected that the microcalorimeter EDS system has the potential to open a new area of the X-ray microanalysis of biological samples.