It has been popular to use transmission electron microscopy (TEM) observation for investigating the microstructure of a phase-change optical disk. In the present work, a new method to prepare a plan-view TEM sample from a disk has been developed. In this method, a copper mesh is placed on a specific area of interest in the disk in advance and then the material is thinned down. By employing this procedure, it becomes possible for the first time to obtain foils that contain the specific area. Furthermore, an advanced method to prepare a cross-sectional TEM sample has also been developed, in which elimination of the polymer substrate is followed by ion milling. With this method, it is possible to prepare cross-sectional foils for high-resolution and analytical electron microscopy observations.