The quantitative electron probe microanalysis of oxygen and other elements in variably oxidized titanomagnetites has been used to measure the degree of oxidation in individual grains from margin to center. Low-temperature oxidation processes of titanomagnetite have thus been demonstrated with natural samples. During oxidation, decreases in iron and increases in oxygen and in titanium have been observed. This finding is consistent with previous studies. The oxidation of titanomagnetite proceeds parallel to an equi-Ti/O line rather than equi-Ti/Fe line.