In this paper, we demonstrated that modification with iridium oxide nanoparticles is a simple and effective method to remarkably enhance the photocatalytic activity and stability of CdSe/CdS quantum dots. The modification was conducted by immersing the nanorods into iridium oxide colloidal solution. Open circuit photovoltage decay spectra reveal that the decay rate declines significantly after iridium oxide modification. Through further treatment of the decay spectra, we obtained the electron lifetime in photoelectrode varied with open circuit voltage, which betrays that the electrode with iridium oxide modification shows a magnitude higher electron lifetime compared to the electrode without.