Langmuir-Blodgett (LB) films (nine double layers) of 2-[4-(N-dodecanoylamino)phenyl]-5-(4-nitrophenyl)-1,3,4-oxadiazole on gold were analyzed by means of infrared (IR) ellipsometry followed by theoretical interpretation of the measured spectra in a uniaxial anisotropic layer model. The same material in a KBr pellet was investigated by IR transmission spectroscopy. The evaluation provided data for vibrational band parameters, necessary for elucidation of the molecular orientation. The LB film was then annealed at 130 degreesC since structural changes due to the thermal treatment were expected to occur, and hence the films before and after annealing can serve as model systems with different molecular orientations. The data revealed that the molecules were hydrogen bonded both in a pellet and as LB films. These bonds were only partly disrupted due to the thermal treatment and play the role of an additional factor stabilizing the film structure. After annealing, a change of about 14degrees was calculated from ellipsometric spectra for the head NO2 group orientation with respect to the surface plane, which would provoke a commensurable decrease of the aliphatic chain tilt angle. The presented results demonstrate the capabilities of infrared spectroscopic ellipsometry not only to determine the film optical constants and thickness, but also to probe some aspects of the molecular orientation.