XRD Rietveld analysis has revealed that Dy0.5Sr1.5NiO4 complex oxide is K2NiF4 type compound, tetragraphic unit cell and space group I4/mmm. A site and B site were found to exist disorder defects of about 3% to 7%. The average bond-valences of Mn and Ni in the B sites, which were deduced from bond length by using bond-Valence relation, are about 3.8 and 2.9, respectively. The order of catalytic activity on CO oxidation is as follows: x=0.2>0.4>0.6>0.8>1.0>0.0, The efficiency of CO oxidation for x=0.2 is 80% at 463K and a gas space velocity of 5000h^-^1.

Key words: OXIDATION, CARBON MONOXIDE, X-RAY DIFFRACTION ANALYSIS, MANGANESE OXIDE, NICKEL OXIDE, DOUBLE OXIDE, STRONTIUM OXIDE, STOICHIOMETRY, CATALYTIC ACTIVITY, DYSPROSIUM OXIDE