In the central nervous system of vertebrates, neurons are connected via synapses to form neuronal circuits. The process of synapse formation and remodeling has been studied intensively by light microscopy [ 1 ]. However, in order to reveal the wiring diagram of the brain at synapse level, there are still some technological problems. One of these technological problem is that the resolution of light microscopy is not enough to observe the precise structure of synapses in the central nervous system. Although electron microscopy is a powerful tool for the observation of the synapses because of its high resolution, the conventional method for three-dimensional reconstruction of serial sections by transmission electron microscopy requires a lot of time and effort and it seems not suitable for connectomical study. Therefore, new technologies are required for large volume 3D reconstruction of the brain. Recent technological advances of scanning electron microscopy (SEM) allow us to overcome this problem [ 2 ]. ATUM (Automated Tape-collecting UltraMicrotome) is one of such a newly-developed technologies to facilitate large volume three-dimensional reconstruction of biological tissue [ 3 ]. By using ATUM, serial sections from ultramicrotome are collected automatically on the plastic tape and are observed by SEM after the tape with sections is glued on a silicon wafer and is coated with carbon. One of the advantages of ATUM is that the sections are preserved on the plastic tape and can be observed repeatedly and it will be advantageous for the correlative observation the samples by both electron and light microscopy. In this symposium, we would like to introduce our approach to the ulrtrastructural analysis of the neural tissue by using ATUM.