A novel catalyst composition for vapor-phase oxidation of butenes which is active at a temperature in the range from 250* to 450*C and capable of converting n-butenes and iso-butene selectively into 1,3-butadiene and methacrolein, respectively. The said catalyst composition contains tungsten, molybdenum, tellurium, antimony and oxygen, one combination selected from among (a) nickel and cobalt, (b) nickel and iron, (c) nickel, cobalt and bismuth and (d) nickel, iron and bismuth, and at least one member selected from the group consisting of potassium, rubidium and cesium. Phosphorus and/or tin may also be added to the catalyst composition.