We report synthesis and characterization of ultrathin cobalt sulfide nanoflakes (CoSx-NFs) sensitized zinc oxide nanorods (Z-NRs) array based thin films and their implementation as photoanodes for photoelectrochemical (PEC) splitting of water. Cobalt sulfide nanoflakes-sensitized zinc oxide nanorods (CoSx-NFs/Z-NRs) array based photoanodes were grown on fluorine-doped tin oxide substrate by a simple and versatile electrodeposition method. Maximum conversion efficiency of PEC cell was found 0.37% with a photocurrent density of 0.48 mA/cm2 at a bias of 0.3 V/SCE in CoSx-NFs/Z-NRs-15 (loading of CoSx-NFs on Z-NRs by cyclic voltammetry for 15 cycles) based photoanodes. The photo-activity is 2.7 times larger than that of Z-NRs array-based photoanode. Experimental results reveal that sensitization by CoSx-NFs causes red shift in the band gap energy of Z-NRs photoanode. Lower band gap energy, suitable band redox potential, and marked absorption in visible light make CoSx-NFs/Z-NRs-15 thin films a promising material for photoanodes in PEC cells. A detailed analysis using X-ray diffraction (XRD), UV-Visible (UV-Visible) spectroscopy, field emission scanning electron microscope (FE-SEM), energy-dispersive analysis (EDX), electron impedance spectroscopy (EIS), Mott-Schottky (MS) analysis, applied bias photon-to-current conversion efficiency (ABPE), and incident photon to current conversion efficiency (IPCE) measurements has been carried out to substantiate our observations. The excellent performance of CoSx-NFs/Z-NRs allows the composite photoelectrode to have many potential applications as a photoanode material for H2 production, nanoflakes-sensitized solar cells, and UV photodetector. © 2017, Springer-Verlag Berlin Heidelberg.