The molecular orientation and chiral properties of the S-citronelloxy-cyanobiphenyl and 4(')-hexyloxy-4-cyanobiphenyl monolayer at the air-water interface were investigated with optical second-harmonic generation (SHG) and Maxwell displacement current (MDC) measurements during monolayer compression. MDC was used to detect the phase transition from planar alignment phase to polar orientational phase in monolayers, and SHG was used to detect the orientation and the chirality of monolayers. The vectorial formulas for the SH process of the monolayer composed of chiral molecules were expressed using tensor components of the nonlinear optical (NLO) susceptibility, where the relationship between the NLO susceptibility and the molecular hyperpolarizabilities was also derived. According to the experiment, a polarized angle dependence measurement could reveal the chirality of this monolayer. The tensor component of the second-order NLO susceptibility, which is related to the chirality of the monolayer, was confirmed to be quite small by a fitting of the polarized angle dependence results, and it was also reasonably supported from the nonlinear molecular hyperpolarizabilities obtained from the quantum chemical calculation. (C) 2003 American Institute of Physics.