Molecular arrangement of polymerized n-octadecyltrichlorosilane (OTS, CH3(CH2)(17)SiCL3) monolayer transferred onto hydrophilic substrate by an upward drawing method was investigated with a transmission electron microscope (TEM) and an atomic force microscope(AFM). The electron diffraction (ED) pattern of the OTS monolayer revealed that the OTS molecules were regularly arranged in a hexagonal array with a (10) spacing of ca. 0.42 nm. The high-resolution AFM image of the OTS monolayer in a scan area of 10 x 10 nm(2) exhibited the individual methyl group of which packing was a hexagonal array in a similar molecular arrangement concluded on the basis of the ED study. Also, the point defect in the crystalline OTS monolayer was successfully observed for the first time.