A very effective metal complex catalyst for the liquid-phase oxidation of saturated hydrocarbons with hydrogen peroxide in an acetonitrile medium is described for the first time. It is supposed that catalytically active species produced from the trinuclear osmium carbonyl olefin complex Os-3(CO)(11)(eta(2)-PhCOCH=CHCOPh) upon its interaction with hydrogen peroxide at 50-70 degrees C efficiently generate hydroxyl radicals, which attack a dissolved alkane and, thus, lead to its oxidation. The turnover number reaches 2400.