Iron absorption efficiency study is one of the key steps to overcome iron deficiency anemia. Determination of iron isotope ratios is the base of iron absorption study. For this purpose radioactive isotope trace method, neutron activation, and thermal ionization mass spectrometry etc. have been used as accessory means. A double focusing inductively coupled plasma mass spectrometry (DF-ICP-MS) was used to determine isotope ratios of Fe in food and human faeces in this paper. Interferences of 40Ar16O to 56Fe and 40Ar14N to 54Fe were avoided by using higher resolution (3000). Longer times and fast electronic scanning were employed to decrease the influence of signal fluctuations from the plasma. Instrumental parameters of the mass spectrometer were optimized while keeping the total integral time under 27s. RSD values obtained for isotope ratios of 5Fe/56Fe, 57Fe/56Fe and 58 Fe/56Fe were 0.23%, 0.14%, 0.22%, respectively, for a natural standard solution of 5 microg x mL(-1). The method has been used to iron nutrition studies.