Imidazole based cobalt (Co) complex (Co-MIm), constructed by the coordination between a heteroaromatic ligand and a transmission metal that cherishes a low overpotential, strong electronic transmission capability and thereby acts as a cocatalyst in photochemical and electrochemical systems, was exploited here to cover a rod structure BiVO4 electrode via a simple in-situ deposition method for photoelectrochemical (PEC) water splitting. The SEM, TEM and XPS characterization suggest that the nanocomposites are consisted of BiVO4 nanorods and Co-MIm species. Under optimized conditions, the composite photoelectrode gave a photocurrent density of 3.16 mA cm(-2) at 1.23 V vs. RHE with a cathodic shift of 230 mV in the photocurrent onset potential, ca. 240% enhancement in comparison to that of pure BiVO4 (1.33 mA cm(-2) at 1.23 VRHE). In the assistance of Co-MIm, both the charge separation and injection efficiencies of BiVO4 photoanode were improved.