Modification of CuFe2O4 catalyst for the simultaneous NOx-soot removal has been studied by doping alkali metals (Li, Na, K, Cs), vanadium and platinum. In pre-doped catalysts, designated as Cu(1-x)A(x)Fe(2)O(4) (A : dopant), potassium was superior to the other alkali metals and vanadium with respect to enhancing the activity and selectivity to NOx reduction into N-2, and the optimum doping level of potassium was x = 0.05. Such a promotion effect of potassium was also observed with the impregnated 5 mol% K/CuFe2O4 catalyst. The impregnation of platinum to CuFe2O4 and Cu0.95K0.05Fe2O4 resulted in a decrease in the selectivity to N-2 formation with the activity being almost unchanged. The high catalytic performance, especially high selectivity, was realized only when the proper amount of potassium is doped in the Cu-Fe spinel catalyst. XPS analysis showed the segregation (enrichment) of potassium on the surface, and too much doping of potassium might cause the covering of active sites of the Cu-Fe spinel oxide.