In this paper, Co3O4 with different morphologies of nanowires (NWs) and nanolayers (NLs) and Ag modified Co3O4 are prepared on ITO substrate via a facile and low-cost hydrothermal successfully. Co3O4/Ag composite structure served as photocathode applied in photoelectrochemical (PEC) water splitting presents efficient PEC activity for the first time. The enhanced optical and photoelectrochemical performance are characterized, the role of Ag nanoparticles is discussed. The photocurrent densities of Co3O4/Ag NWs and Co3O4/Ag NLs are up to -4.73 mA cm(-2) and -4.26 mA cm(-2), respectively. The improved PEC performance is attributed to a high light-harvesting efficiency, an expanded photoresponse range, accelerated holes mobility and increased interfacial photoelectrons transport of Ag nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.