Abstract: The present invention intends to mount and preserve a thin section prepared from a freeze-embedded sample using an adhesive plastic film as a support for the thin section, in a state of being attached to the adhesive plastic film, as a permanent specimen that can be observed on an optical microscope, after staining the thin section in a state of being attached to the adhesive plastic film. For this purpose, using an adhesive plastic film having a strong adhesion even at a lower temperature (e.g., ?25° C.), a thin section that is kept in its shape is prepared. Subsequently, the thin section is stained while being attached to the adhesive plastic film. After that, the thin section is permeated with a water-soluble resin that can be polymerized upon irradiation with light or heating. The thin section is closely attached to a glass plate having the same resin coated thereon, and is then irradiated with light or heated, thereby causing polymerization of the water-soluble resin.