The initial stages of the liquid-phase oxidation of cyclooctene with molecular oxygen were studied in the presence of Mn3O4. It was found that the catalyst did not affect the chain propagation and termination steps. The radicals are generated in the reaction system via interaction of the olefin with the catalyst surface. At a high degree of advancement of the reaction, catalytic decomposition of the hydroperoxide formed can contribute to the overall rate of radical generation. The kinetic parameters of the reaction were determined.