Molecular arrangement of two kinds of Langmuir-Blodgett monolayers composed of poly(N-dodecylacrylamide) and N-octadecylacrylamide win characterized with the atomic force microscope (AFM), The dodecyl side chains in the polymer Langmuir-Blodgett monolayer were observed as random molecular arrangement. In contrast, alkyl chains in N-octadecylacrylamide monomer Langmuir-Blodgett film were highly ordered to form two dimensional crystals. The X-ray diffraction patterns of the monomer and polymer Langmuir-Blodgett films were consistent with the AFM observation. The polymer Langmuir-Blodgett monolayer was not destroyed by AFM tip scanned in the contact mode, indicating that the monolayer is mechanically appreciably stable.