High-quality Cu2O nanowire (NW) photocathode was successfully fabricated upon annealing Cu(OH)(2) NW precursor. The precursor was prepared via a wet chemical oxidation method [Cu foil + (NH4)S2O8 + NaOH] which is always accompanied with unfavourable nanostructured CuO. However, the present study has synthesized the precursor without the emergence of CuO with modified growth solution at room temperature. Under proper growth condition, the height and width of pure, vertically erected Cu(OH)(2) NW has increased proportionally to the ageing time for growing NW. The photoelectrochemical (PEC) measurement of Cu2O NW under 100 mW cm(-2) light irradiation and 0.5 M Na2SO4 electrolyte solution, has generated - 5.45 mA cm(-2) at - 0.6 V vs. Ag/AgCl. The high photocurrent density was attributed to the high carrier density (2.69 x 10(21) cm(-3)) accompanied with a low charge transfer resistant under illumination. The inexpensive and highly scalable Cu2O NW is a promising photocathode for PEC solar to energy application.