Solar wind abundance ratios of magnesium isotopes measured with the high resolution Mass Time‐of‐Flight spectrometer (MTOF) of the Charge, Element, and Isotope Analysis System (CELIAS) experiment on board the Solar and Heliospheric Observatory (SOHO) are presented. MTOF, as part of CELIAS, is, because of its high time and mass resolution, an excellent tool for isotope abundance measurements in the solar wind. From the data analysis we have found that the isotopic composition of magnesium in the solar wind agrees with the terrestrial composition within the experimental uncertainty. We have obtained isotopic ratios of 24Mg/25Mg = 7.7 ± 0.4 and 24Mg/26Mg = 7.0 ± 0.5. These values are consistent with the terrestrial values of 24Mg/25Mg = 7.90 ± 0.01 and 24Mg/26Mg = 7.17 ± 0.03. Furthermore, these investigations also show that with the given uncertainties the abundance ratios do not vary significantly within a solar wind velocity range from 375 km/s to 530 km/s.
