A series of Ru-Ir bimetallic catalysts with different mass ratios (Ru-Ir/TiO2, Ru:Ir = 9:1, 7:3, 5:5, 3:7, 1:9) were prepared by iso-volumetric impregnation method. The activities of the catalysts for simultaneous removal of soot and NOx were investigated by Temperature Programmed Surface Reaction (TPSR) technique, and the properties of the catalysts were characterized by various analysis techniques, such as XPS, XRD, TEM, H-2-TPR, H-2-TPD and nitrogen adsorption. The results indicated that Ru-Ir/TiO2 bimetallic catalysts had better activity for simultaneous removal of soot and NOx than Ru/TiO2 or Ir/TiO2. When the mass ratio of Ru:Ir was 9:1, the catalyst showed the best catalytic activity. The peak temperature of soot oxidation was 437 degrees C and the highest conversion efficiency of NO,, was 42.6%. On the basis of the characterization of the catalysts, the relationship between the catalytic activity of Ru-Ir/TiO2 and the synergetic roles of Ru and Ir was discussed.