To utilize Si nanostructures as photocathode for high-efficiency solar water splitting, a catalyst with low cost and high activity is inevitable to modify Si. In this study, employing the electrochemical deposition method, the surfaces of Si nanowire arrays were decorated with a novel non-noble metal electrocatalyst, Mo4O11. The morphology, chemical composition and structure of the as-synthesized Si/Mo4O11 nanowire arrays were characterized in details. As photocathodes for photoelectrochemical water splitting, the Si/Mo4O11 nanowire arrays exhibited more positive turn-on potential and larger photocurrent compared to Si nanowire arrays. The results demonstrate that the Si/Mo4O11 nanowire arrays could be a promising candidate for solar water splitting.