Monolayers or bilayers of the azobenzene derivative 4-octyl-4’-((carboxyltrimethylene)oxy)azobenzene (ABD) have been deposited by the Langmuir-Blodgett (LB) method on gold substrates modified with thiol self-assembled monolayers. Here the thiol monolayer serves both as a substrate for the LB film and as a barrier for the electron transfer between the azobenzene and the gold substrate. The electrochemical properties of the ABD films depend on the length of the thiol molecule and the orientation of the ABD molecule. They become more irreversible when the thiol molecule is longer and when the ABD molecule is adsorbed on the thiol with its hydrophobic terminal. Although energetically unstable cis-ABD is reduced to the hydrazobenzene derivative (HBD) at a more anodic potential than trans-ABD, the reduction of cis-ABD was not observed in the cyclic voltammetry of ABD films on 2-mercaptoethanol. Moreover, UV light irradiation of the trans film in a certain cathodic potential range causes cathodic and anodic spikelike currents when the light intensity is increased and decreased, respectively, at the cathodic bias potential. These phenomena are explained by using the following mechanism; i.e., the reduction of cis-ABD can occur at a more anodic potential than the oxidation of HBD when the separation of the redox potentials is relatively small for trans-ABD. If the above two opposite reactions take place much faster than the voltammetric potential scan, the electron flows cancel each other out and no net faradaic current can be observed. However, the spiked current responses are generated when the amounts of reduction and oxidation currents become out of balance.