Photoelectrochemical reduction of CO2 is an efficient way to overcome the limited supply of fossil fuels and mitigate the greenhouse effect, as well as produce carbonaceous fuels from the sunlight. CuBi2O4 is a p-type semiconductor with conduction band potential negative enough for CO2 reduction. Nanoporous CuBi2O4 photocathodes are prepared by electrodeposition with subsequent annealing and are comprised of well-crystallized nanoparticles, which exhibit good visible-light response. The film thickness can be adjusted readily by changing the deposition time. The charge behavior in the CuBi2O4 photocathodes and its relationship with the film thickness are thoroughly investigated by using photocurrent and intensity modulated photocurrent spectroscopy. It is found that CuBi2O4-4 min possesses the optimized charge generation and transfer performance, and shows the highest activity with CO as the only product of photoelectrochemical reduction of CO2 under 0 V vs Ag/AgCl. The results indicate that CuBi2O4 can be a promising photocathode for CO2 photoelectrochemical reduction under low bias.