Simple electrodeposition method was employed for the fabrication of platinum-ruthenium bimetallic nanoparticles (PtRu NPs) modified poly(3,4-ethylenedioxythiophene) (PEDOT) coated on the indium tin oxide (ITO) at room temperature. The formation mechanism of PtRu NPs film is monitored by cyclic voltammetry (CV) techniques and atomic force microscopy (AFM). It is found that PtRu NPs/PEDOT/ITO photo cathode increased the reactive interface, which supports charge transfer at the interface and had higher electrocatalytic activity for the I3−/I− redox reaction and a smaller charge transfer resistance than the Pt/ITO photo cathode. With a PtRu NPs/PEDOT/ITO photo cathode as a counter electrode of DSSC, a 16.5% improvement in the cell efficiency is achieved.