Twelve zeolite catalysts partly modified with 10% Cr or 5% Fe oxides were prepd. by wet impregnation and tested in the selective catalytic oxidn. of NH3 to N-2 and H2O. Phys.chem. properties of the catalysts were detd. by temp.-programmed redn. and X-ray diffraction. The Cr-modified catalysts showed the same high activity in the studied reaction at above 300 degrees C, where 100% conversion of NH3 was achieved.