We fabricated a CZTS electrode by the sol-gel and spin-coating method on an Mo/glass substrate and performed photoelectrochemical (PEC) reduction of nitrobenzene (NB) in an aqueous environment under visible light irradiation (420 < lambda < 800 nm). By using the CZTS electrode, a six-electron reduction reaction of NB to aniline (AN) proceeded in an aqueous solution under visible light irradiation. We found that NB reduction reaction was strongly dependent on the electrode potential; large cathodic polarization is kinetically favorable for hydrogen evolution over a CZTS electrode, which leads to hindrance of the PEC NB reduction reaction, resulting in a decrease in the yield of AN (< 20%). At small cathodic polarization, conversion of NB reached to > 99% and the yield of AN was calculated to be > 50%. Moreover, we found that the proton concentration in an aqueous electrolyte had a significant effect on the PEC NB reduction reaction. In this study, we investigated the PEC NB reduction reaction over a CZTS electrode in conjunction with the structural and optical properties.