The catalytic properties of the systems based on bismuth, cobalt, and iron molybdates in the oxidation of isobutylene to alpha -methylacrolein were examined. The data on oxygen chemisorption kinetics on the catalysts were obtained. The mechanism of partial oxidation of the olefin was studied in the pulse reaction mode. The bismuth molybdate phase was shown to be mainly responsible fur the selectivity of the catalytic action. The iron and cobalt molybdate phases were shown to ensure the high rate of the hydrocarbon chemisorption on the catalyst surface. A likely source of carbon dioxide may be the deep oxidation of alpha -methylacrolein and the methacrylic acid formed.