An archaeological waterlogged polypore was found in the Final Jomon period (circa 2600 years ago) at the Neolithic site of Kitashirakawa in Kyoto, Japan. The fragile polypore was treated with the feather-keratin method that we developed for the preservation of wet organic archaeological materials. The method reinforced the polypore against the collapse caused by air-drying. The anatomical features of the polypore were observed under light microscopy and the host wood present at the edge of the basidiocarp was identified as Morus sp. on the basis of anatomical observations. Eventually, the polypore was identified as Inonotus sanghuang. Macroscopic and microscopic observations were carried out in order to evaluate the effectiveness of the keratin treatment on the polypore tissue. The keratin consolidated to the hyphal cell walls, where it stabilized the thick walled fungal mycelium that makes up the polypore fruiting body.