UV-visible absorption spectroscopy and Fourier transform infrared reflection absorption spectroscopy were utilized as in situ probes to investigate the electrochemical redox process in an azobenzene-terminated self-assembled monolayer (SAM) film in an aqueous electrolyte. The electrochemical reduction process, which is exceedingly slow due to disruption of the extremely densely packed SAM, produced the hydrazobenzene species. Upon reoxidation, the resulting hydrazobenzene is quickly converted back to trans-azobenzene, It appears that the electrochemical redox process is accompanied by a reversible orientational change in terms of the azobenzene terminal group. Therefore, by simply modulating the applied potential, a reproducible electrochemical redox process together with a reversible orientational variation can be achieved in an organized monolayer film.