Manganese porphyrin catalysts with different number of halogens atoms substituted at the phenyl and pyrrole rings were investigated in the Lyons system in oxidation of cyclooctane with molecular oxygen (as air) to cyclooctanone and cyclooctanol without the use of sacrificial co-reductant. The catalytic activity of metalloporphyrins increases with the increase of the redox potential of metalloporphyrins in the investigated system and shows almost linear relationship with the number of the halogens on porphyrin macrocycle. On the basis of obtained results the new reaction mechanism is discussed and proposed. (C) 2002 Elsevier Science B.V. All rights reserved.