Optical Second Harmonic Generation (SHG) and Maxwell displacement (MDC) spectroscopy for the exploration of organic monolayer film is described. MDC and SHG are ascribed to tire surface spontaneous and non-linear polarization of the monolayers due to symnetry breaking, respectively. It is shown. that the ShG-MDC measurement, cow be used for the study] of the orientational orders. In order to show lite effect of the SHG-MDC spectroscopy, the, dielectric polarization of monolayer with C-infinity-symmetry is theoretically analyzed with a simple rod-molecule model, and the surface polarization induced in the monolayer is expressed using orientational order parameters. The SHG and MDC generated from mesogenic liquid crystal (LC) monolayers are shown, and discussed based on the developed theory.