The dielectric polarization of organic monolayers at the air-water interface has been analyzed, assuming that the monolayers have C-infinity symmetry. The formula of polarization of organic monolayers is derived and it is expressed using orientational order parameters. It is shown that Maxwell-displacement current measurement coupled with optical second harmonic generation measurement is helpful for the determination of these orientational order parameters. Monolayers of 4'-n-pentyl-4-cyanobiphenyl on the air-water interface were examined during monolayer compression and the orientational order parameters were determined.