Microstructural and microanalytical investigations were carried out for traditional Japanese clay ceramics called Sekishu-kawara. In this study, optical microscopy as well as scanning- and transmission-electron microscopy were employed. Specimens under investigation are (A) the original wet materials dried in air for several days, (B) the materials dried at 773 K, and (C) the same materials fired and sintered at 1493 K in a tunnel kiln. Not only some clear SEM images but also the TEM images, which were taken for the first time by us, for the clay ceramics are presented. TEM mi-crographs of specimen C show that mullite crystals, grown in the firing and sintering process, are in the shape of strip, 5 nm×50 nm×500 nm in largest, and are dispersed, in the amorphous glass. SEM micrographs of specimen C, on the other hand, show that the clay ceramics are porous and contain considerable amount of tunnel-shaped open spaces called continuous pores. The continuous pores are constructed by a complicated, three dimensional shape of amorphous glass, in which the mullite strips exist.