The molecular orientations in N-octadecylacrylamide, nonadecylacrylamide and icosylacrylamide Langmuir-Blodgett (LB) films, which show high capability of the polymerization, are investigated by Fourier transform infrared (FTIR) measurements. A jra tic IR dichroism caused by the considerable anisotropic arrangement of these N-alkylacrylamide molecules alone the dipping direction was observed. It is found from the comparison with the FTIR spectra of some amphiphile derivatives that the in-plane orientation in these alkylacrylamide LB films is characteristic of the acrylamide chemical structure.