Human enamel tufts appeared as corrugated ribbon-like structures located on the dentin parallel to the tooth axis when observed under the binocular microscope and scanning electron microscope (SEM). SEM observation disclosed enamel tufts as bundles of well-extended tubular structures attributable to hypomineralized enamel sheaths. Plate-like structures, previously referred to as “tuft-root” ran in the center of the enamel tufts, connecting the dentin surface. When observing under the transmission electron microscope, the plates of tufts extended from the superficial layer of the dentin, penetrating the hypermineralized zone adjacent to the dentin-enamel (D-E) junction, and then, reaching the tuft region. In the tuft region, the plates of tufts ran mainly along the enamel sheaths and partially across the enamel prisms. The immuno-gold technique verified an intense immunoreactivity for amelogenin in the superficial layer of the dentin as well as the enamel prisms in the tufts, although no reaction was found over the “plates of tufts”. The immunoreactivity for 13–17 kd sheath proteins, also denoted as sheathlin, ameloblastin or amelin, was detected over the filamentous structures closely associated with the enamel sheaths in the enamel tuft. Thus, our study demonstrated that enamel tufts consist of both well extended hypomineralized enamel prisms and “plates of tufts”. The major organic substance of the enamel tufts is suggested to be 13–17 kd sheath proteins rather than amelogenin. © 2005, Japanese Association for Oral Biology. All rights reserved.