Co3O4/In2O3 nanocomposites were prepared via a microwave-hydrothermal method and directly used as photoanodes for the photoelectrocatalytic (PEC) process to reduce Cr(VI). The as-prepared Co3O4/In2O3 composites show a rod-like structure, which is composed of nanoparticles. The PEC experiments indicated that after 120 min of irradiation with 0.7 V bias voltage and visible light, the Cr(VI) reduction efficiency of Co3O4/In2O3 composites in aqueous solution was 100%, which was superior to the samples prepared by other methods. Moreover, the Co3O4/In2O3 composite still had a high catalytic activity after five runs of PEC experiments. Elimination experiments demonstrate that photo-generated electrons (e–) performed a key role in the catalytic reduction of Cr(VI). The significantly improved PEC performance can be attributed to the bias voltage and the p-n heterojunction formed between Co3O4 and In2O3. Therefore, Co3O4/In2O3 nanocomposites have a considerable potential for the PEC reduction of Cr(VI).