The molecular orientation of liquid crystals mixed with stearic acid-d(35) in Langmuir-Blodgett (LB) films on the polyion complex with azobenzene-containing fatty acid and polycation was examined using Fourier transform infrared (FTIR) reflection-absorption (RA) and UV-Vis spectra. It was found from UV-Vis measurements that the polyion complex in these LB films shows reversible photoisomerization when irradiated by UV or visible light. Further, changes in the RA spectra revealed that the orientation of molecules in liquid crystal mixed with stearic acid-d(35) is controlled by the trans-cis photoisomerization of the polyion complex at 45 degrees C, but their orientation is unaffected at 25 degrees C. This result can be explained by the difference in the state of the liquid crystal at these different temperatures.