A highly enhanced activity for photoelctrochemical water splitting was achieved by fabricating a carbon nanotube (CNT) and Co3O4 decorated hierarchical ZnO nanowire (NW) arrays via a facile stepwise synthesis strategy. The ternary CNTs-ZnO-Co3O4 NWs composite exhibits an increased photocurrent density (1.9 mA cm-2 at 0.6 V vs. Ag/AgCl, 2.7 times larger than the pristine ZnO NWs ), improved incident photon to current conversion efficiency (52.5% at 340 nm, 5.1 times higher than the pristine ZnO NWs) as photoanode under AM 1.5G simulated sunlight. This enhancement is attributed to the specific heterogeneous ternary architecture, which evolved a promoted electron-hole charge separation and transfer, decreased water oxidation overpotential as well as increased reaction rates of water splitting by decorating ZnO NWs with CNTs and Co3O4.