Catalytic oxidative modification of single-stranded DNA with hydrogen peroxide and molecular oxygen in the presence of a conjugate containing an oligonucleotide complementary to the DNA fragment and tetra-4-carboxyphthalocyanine Fe(II) was studied. The conjugate examined was found to be active in the reaction of oxidative DNA cleavage in the presence of hydrogen peroxide, like earlier studied oligonucleotide conjugates containing tetra-4-carboxyphthalocyanine Co(II) and 2,4-di-[2-(2-hydroxyethyl)]deuteroporphyrin IX Fe(III) metallocomplexes generating active oxygen forms. The new conjugate was more active in the case of oxidation with molecular oxygen. Kinetic regularities and optimal regimes of DNA oxidation with hydrogen peroxide were found.