The dehydroxylation of kaolinite was investigated in detail by means of energy-filtering transmission electron microscope with both orientations parallel and perpendicular to c. The dehydroxylation could be characterized by the broad background including (0.211) band (20~24$^{circ}$ 2$ heta$) on X-ray diffraction and by the three halo rings (d-spacing : 3.28~4.40$AA$ (near (02,11) band), 2.41~245$AA$ (near (20,13) band), 1.16~1.23$AA$ (near (0.8,44) band)), and (02,11) and (20,13) spots on electron diffraction. These indicate existence of a short-range order along the a and b axes. Interplanar spacing of (001) is reduced to about 6.86$AA$ and the sharp additional intensity maximum of about 14.2$AA$ reveals that metakaolinite has a modulated structure along c axis. It is proposed that the modulated structure is attributed to the domains consisting of more than two-layers due to the changes of positions of the vacant octahedral sites in successive layers.