Clay mineral specimen for electron microscopy have usually been prepared by air-drying of a small drop of the suspensoin on a microgrid. The suspension method is, however, not always preferable for the observation of lattice images of clay minerals because of their preferred orientation in the air-drying process. The present writers proved that the embedding method is excellent in preservation of the nonorientated part of the crystal than that of susp, ension method. The interstratified kaolin/montmorillonite which was collected from clay bed at Itoigawa, Niigata prefecture is dehydrated progressively replacing H(2)O by ethanol, propylene oxide and Epon mixture solution and is lastly embedded in Epon 812. Ultra-thin sections are prepared with an LKB Ultratome, and are examined in a JEM-100C type electron microscope at an accelerating voltage of 100 kV. High resolution electron micrographs show lattice images reflecting irregular layer structures of kaolin and montmorillonite. Clear layer structure and lattice images can be well observed from everywhere of ultra-thin section of clay mineral (Fig. 1). Lattice images of 4.5 and 10A spacings can be observed in Fig. 2. Microstructures show some differences in spacing which emerged from combination of dehydrated montmorillonite and kaolin layers (Fig. 3).