Abstract: The relationship between the activity of La-Ce Catalysts and molar ratio of La-Ce was studied in the paper. These catalysts were prepared by impregnation method using cordierite holeycomb monoliths obtained from Yixing coated by γ-Al₂O₃ as carrier. The effect of the molar ratio of La-Ce on the property of Pd-TWC was also studied. consults showed that the catalytic astivity of Pd-TWC in Purifying CO, HC and NO varied with the ratio of La-Ce. The best catalytic activity was obtained when the ratio was l:4. Under this circumstances, the amount of resodual oxygen on its surface was largest. XPS results showed that Ce⁴⁺ coexited with Ce³⁺ and the relative amount of Ce⁴⁺ is the biggest in all the samples and equaled 60%. La and Ce had a synergestic action on improving catalytic astivity of Pd-TWC.