Great efforts have been paid to improve the photoelectrochemical performances of FeVO4 semiconductors. However, there have rarely been reported about the modifying of FeVO4 with metal-free co-catalyst for enhanced photoelectrochemical activities. Herein, we demonstrate a facile and effective immersion method for coupling ultrathin g-C3N4 nanosheets with nanoporous FeVO4 photoelectrodes. The FeVO4/g-C3N4 heterostructures demonstrate more than twice higher photocurrent density than pure nanoporous FeVO4 photoelectrodes, which should be attributed to the metal-free co-catalyst of ultrathin g-C3N4. It is believed that the ultrathin g-C3N4 nanosheets can effectively trap the photo excited holes and facilitates the charge separation efficiency and thus significantly improve the photoelectrochemical performances of FeVO4. [GRAPHICS]