The Langmuir film behavior of an amphiphilic thermotropic mesogen at the air-water interface has been studied from surface pressure-molecular area isotherms. The isotherms exhibited a transition from an expanded to a condensed phase and on further compression also indicated the formation of an unstable monolayer, evidenced through a pronounced hysterisis observed during the decompression cycle. This phenomenon is explained on the basis of stronger hydrophobic forces dominating the orientation in the condensed phase. Increase in the limiting molecular area at lower temperatures provides supporting evidence for the observed loss of a stable condensed phase, which is attributed to the dissolution of the molecules into the aqueous subphase.